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SEISMOGENIC FAULT AND COSEISMIC SURFACE DEFORMATION OF THE DINGRI MS6.8 EARTHQUAKE IN XIZANG, CHINA SHI Feng, LIANG Ming-jian, LUO Quan-xing, QIAO Jun-xiang, ZHANG Da, WANG Xin, YI Wen-xing, ZHANG Jia-wei, ZHANG Ying-feng, ZHANG Hui-ping, LI Tao, LI An SEISMOLOGY AND GEOLOGY    2025, 47 (1): 1-15.   DOI: 10.3969/j.issn.0253-4967.2025.01.001 Abstract （2357）   HTML （73）    PDF（pc） （13725KB）（1108）       Knowledge map    Save At 09:05 am on January 7, 2025, a MS6.8 earthquake occurred in the Dingri, Xizang, China. The earthquake caused serious casualties and property losses. Research on the seismogenic structure and characteristics of earthquake surface rupture in this earthquake is beneficial to understanding the rupture behavior and dynamic mechanism of normal-fault earthquakes. Meanwhile, it provides a basis for predicting the future strong earthquake trend of the southern Xizang rift fault system. Its epicenter is located at 87.45°E, 28.50°N, 13km depth, the China Earthquake Networks Center measures. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake. This preliminary study finds that the seismogenic fault of the Dingri MS6.8 earthquake is the Dengmocuo fault, which is an active ~60km long, NS-NE-striking and normal fault. The total length of the co-seismic surface ruptures is approximately 25km, located on the north segment of the Dengmocuo fault. Meanwhile, a dense deformation zone of ground fracture with a length of ~10km is generated on the east side of Dengmocuo Lake along the contour line of the lake shore. The earthquake also induced a large number of liquefaction structures and tensional fractures in valleys and basins. Based on along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into three segments: the Gurong-Qiangga, Nixiacuo, and Yangmudingcuo segments. The surface ruptures are relatively continuous and prominent along the Nixiacuo segments. Comparatively, co-seismic surface ruptures of Gurong-Qiangga and Yangmudingcuo segments are discontinuous. The maximum of coseismic vertical displacement is roughly determined to be 2.5—3.0m based on the scarps. The width of the surface rupture zone of the Dingri earthquake can reach up to 450m in some areas. The location of surface rupture zones is not limited to fault scarps and hanging walls. There are also a large number of secondary scarps and cracks distributed in the footwall. Many cracks are distributed in an en echelon or grid pattern. Compared to the continuous surface rupture caused by strike-slip-type earthquakes in recent years, the surface rupture of the Dingri earthquake is very discontinuous, and there is an obvious difference in displacement between each segment of the surface rupture. Preliminary speculation suggests that it may be related to the characteristics of the fault movement. Unlike strike-slip faults where the dislocation direction is parallel to the strike, the dislocation direction of normal faults is perpendicular to the strike. In addition, the observed length of surface rupture and maximum displacement of the Dingri earthquake are basically consistent with the results calculated by empirical formulations. Table and Figures | Reference | Related Articles | Metrics

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GEOLOGICAL DISASTERS AND SURFACE RUPTURES OF JANUARY 23, 2024 MS7.1 WUSHI EARTHQUAKE, XINJIANG, CHINA ZHANG Bo-xuan, QIAN Li, LI Tao, CHEN Jie, XU Jian-hong, YAO Yuan, FANG Li-hua, XIE Chao, CHEN Jian-bo, LIU Guan-shen, HU Zong-kai, YANG Wen-xin, ZHANG Jun-long, PANG Wei SEISMOLOGY AND GEOLOGY    2024, 46 (1): 220-234.   DOI: 10.3969/j.issn.0253-4967.2024.01.013 Abstract （1623）   HTML （79）    PDF（pc） （14676KB）（853）       Knowledge map    Save The MS7.1 earthquake in Wushi, Xinjiang on January 23, 2024, represents the largest earthquake in the Tianshan seismic belt since the 1992 Suusamyr MS7.3 earthquake in Kyrgyzstan. Preliminary precise aftershock localization and initial field investigations indicate an NE-trending aftershock zone with a length of 62km that is concentrated at the mountain-basin transition area. This event produced geological hazards, including slope instability, rockfalls, rolling stones, and ground fissures, primarily within a 30-kilometer radius around the epicenter. The epicenter, located approximately 7 kilometers north of the precise positioning in this study, witnessed a rapid decrease in geological hazards such as collapses, with no discernible fresh activity observed on the steep fault scarp along the mountainfront. Consequently, it is inferred that the causative fault for this main shock may be an NW-dipping reverse fault, with potential rupture not reaching the surface. Moreover, a surface rupture zone with a general trend of N60°E, extending approximately 2 kilometers, and displaying a maximum vertical offset of 1m, was identified on the western side of the micro-epicenter at the Qialemati River. This rupture zone predominantly follows the pre-existing fault scarp on higher geomorphic surfaces, indicating that it is not new. Its characteristics are mainly controlled by a southeast-dipping reverse fault, opposite in dip to the causative fault of the main shock. The scale of this 2-kilometer-long surface rupture zone is notably smaller than the aftershock zone of the Wushi MS7.1 earthquake. Further investigation is warranted to elucidate whether or not the MS5.7 aftershock and the relationship between the SE-dipping reverse fault responsible for the surface rupture and the NW-dipping causative fault of the main shock produced it. Table and Figures | Reference | Related Articles | Metrics

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APPLICATION OF DEEP LEARNING IN ACTIVE TECTONICS AND GEOMORPHOLOGY LIU Xin, WANG Shi-rou, SHI Xu-hua, SU Cheng, LU Chen-yan, QIAN Xiao-yuan, SUN Qiao-yang, DENG Hong-dan, YANG Rong, CHENG Xiao-gan SEISMOLOGY AND GEOLOGY    2024, 46 (2): 277-296.   DOI: 10.3969/j.issn.0253-4967.2024.02.003 Abstract （590）   HTML （37）    PDF（pc） （5210KB）（680）       Knowledge map    Save The research on active tectonics and geomorphology involves extensive sub-topics, including the kinematics of crustal movements, the processes underlying the evolution of landforms, and the associated dynamic mechanisms. These sub-topics are intricately connected with the interactions between the Earth’s endogenic and exogenic processes. In the contemporary realm of the Earth system science, research in active tectonics and geomorphology has become a hot topic for interdisciplinary study. The advancement in big data research coupled with the progressive developments in deep learning technologies has furnished this field of study with a voluminous array of data sources and the requisite analytical tools for technical analysis. In recent years, the application of big data and deep learning technologies in this research field has yielded a series of outstanding results, fostering new research directions, and ushering the discipline into a new phase. In this paper we synthesize existing research to outline the data sources pertinent to the study of active tectonics and geomorphology, including field geological survey, unmanned aerial vehicle (UAV)-based photography, aerial photography, and remote sensing observations. Then, we discuss in-depth examination of the recent innovations progresses in deep learning algorithms, including but not limited to convolutional neural networks(CNNs), deep Gaussian processes, and autoencoders. This article further elaborates on innovative applications of deep learning in the study of active tectonics and geomorphology. These include the identification of changes in glacier extent, monitoring volcanic activity and deformation, recognizing river systems, precise surveillance of landslide events, as well as observations of lithospheric deformation co-seismic surface ruptures. Based on the summary of prior studies, this paper showcases a distinct application instance. By employing convolutional neural networks(CNNs)within the realm of deep learning image analysis and utilizing UAV-obtained high-resolution images, we undertake the automated detection of structural fractures in granite rocks in Meizhou island, in the southeast of Fujian province, China. In fault damage zones, structural rock fractures are widely developed, and the study of their orientation, system, and secondary characteristics is of great importance for determining their mechanisms of development and the multi-phase tectonic activity events in the region. Under conventional methodologies, the study of structural fractures in rocks is time-consuming and requires considerable manual effort in conducting exhaustive field surveys and detailed interpretation of cartographic representations. However, the application of deep learning can greatly enhance the efficiency of cartographic work. This application case has improved the classic deep learning framework by developing a CNN model specifically designed for the extraction of complex features and multi-scale rock fractures. This model achieved rapid identification of over 9 000 fractures with varied shapes and complex distributions within 55 minutes, attaining an accuracy of 85% and a recall rate of 89%. These findings demonstrate that deep learning significantly enhances operational efficiency in comparison to manual statistical methods for the automated identification of rock structural fractures, while also maintaining exceptional accuracy in fracture detection. Based on the results identified by deep learning, it can be clearly observed that two sets of fractures, oriented NE and NW, develop on the granite outcrops in the study area. According to previous research and the cross-cutting relationships of the fractures, it is known that NE-oriented fractures formed earlier than NW-oriented fractures, corresponding respectively to the Indosinian Movement and the expansion movement of the South China Sea in the tectonic history of South China. Through the automated extraction of deep learning models, the workload of manual mapping can be greatly reduced, yielding results consistent with actual geomorphological phenomena. Table and Figures | Reference | Related Articles | Metrics

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GEOMORPHIC DATING OF SCARPS AND ITS APPLICATION TO ACTIVE TECTONICS AND GEOMORPHOLOGY PANG Zhen-hui, XU Hao-ting, SHI Xu-hua, GE Jin, LI Feng SEISMOLOGY AND GEOLOGY    2024, 46 (2): 251-276.   DOI: 10.3969/j.issn.0253-4967.2024.02.002 Abstract （611）   HTML （33）    PDF（pc） （3088KB）（578）       Knowledge map    Save Scarps are typical geomorphic features of tectonics, climatic changes, and erosion processes. On one hand, interpreting geological information encoded in scarps allows for the quantitative constraint of the kinematic and dynamic mechanisms of the active structures. On the other hand, studying the evolution processes of scarps contribute to a better understanding of the couplings among tectonics, erosion, and climate during geomorphic evolution processes. In regions characterized by adverse geological conditions, limited accessibility, and logistical challenges hindering researchers from reaching certain areas, traditional dating methods such as radiocarbon dating, luminescence dating, and cosmogenic nuclide dating often face difficulties in determining the age of scarps. The geomorphic dating method of scarps, however, offers a promising avenue to address the scarcity of chronological samples in research areas where either sample availability is limited or conventional dating techniques are impractical. This paper provides a concise summary of the theoretical evolution of geomorphic dating of scarps. Emphasis is placed on elucidating the slope evolution processes, transport models, and associated computational methodologies integral to this approach. Additionally, the specific applications of these methods in active tectonics and geomorphology are highlighted, accompanied by a case study showcasing their practical implementation. The theoretical foundation of geomorphic dating of scarps posits that the evolution of scarps during stable erosion stages can be simulated through models describing the evolution of slope surfaces over time. In practical dating applications, it is essential to determine the theoretical models and computational methods for the evolution of scarps. This necessitates the integration of measured profiles of the scarp to establish boundary and initial conditions, facilitating the determination of the geomorphic age of the studied scarps. On one hand, the related slope evolution model mainly involves processes such as bedrock weathering, sediment transport, and tectonic uplift. Previous studies have proposed dozens of quantitative slope evolution models and geomorphic transport functions(e.g., local linear, local nonlinear, non-local, etc.)based on various slope processes, theoretical assumptions, and numerical simulations. In various transport equations, compared to earlier local linear models, later local nonlinear transport models proposed based on experimental simulations and physical derivations exhibit higher fitting accuracy for real slope evolution. In the past decade, some scientists have proposed nonlocal transport models because of the limitations of traditional transport models, and have applied them in research. This nonlocal model assumes that the distance of sediment movement within a given area follows a probability distribution, thus allowing the simulation of long-distance slope processes over short periods. Additionally, many other transport models have been derived from specific slope processes, such as biotic disturbance and dry ravel. The solution methods for the aforementioned models vary as well. For instance, the analytical solution of a local linear diffusion transport model can be relatively easily obtained, while local nonlinear models and nonlocal models can only be numerically solved through specific approaches. On the other hand, the measured topographic profiles of the studied scarps can be used to determine the practical parameters of slope evolution models, including the present-day morphology of the scarps and their ages since their initial formation. In practical applications, various methods have emerged for the geomorphic dating of scarps, generally classified into two types based on the approach to fitting model calculations with actual topographic profiles: the mid-point slope method and the full slope method. The mid-point slope method uses the mid-point gradient value as the fitting morphological feature, representing an early method for dating scarps, mostly combined with linear diffusion transport functions and requiring numerous profiles for statistical analysis. Due to its low data utilization and limited spatiotemporal precision in statistical methods, the mid-point slope method has gradually been replaced by the full slope method. The full slope method involves fitting the overall shape of actual profile curves using model solutions. With the continuous improvement of observation techniques in the field of Earth sciences and the deepening research on related theories, the application scope of scarps geomorphic dating methods is no longer limited to the study of terraces and simple fault scarp evolution processes but has expanded to more complex geological environments, providing more precise constraints on their formation and evolution history. For method application, we systematically present the progress in scarp geomorphic dating research across various geomorphic settings(such as river and coastal terraces, lake shorelines, alluvial fans, marine terraces, and extraterrestrial planets). It employs the geomorphic dating of the northeastern Pamir fault scarp as a case study to further explore and anticipate the developmental trajectory of geomorphic dating of scarps within the field of tectonic geomorphology. Table and Figures | Reference | Related Articles | Metrics

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MECHANISM DIFFERENCES BETWEEN SEVERAL TYPICAL PYROCLASTIC ROCKS AND THEIR VOLCANISM SIGNIFICANCE WEI Hai-quan, CHEN Zheng-quan, LIU Yong-shun, BAI Zhi-da SEISMOLOGY AND GEOLOGY    2024, 46 (2): 297-311.   DOI: 10.3969/j.issn.0253-4967.2024.02.004 Abstract （738）   HTML （14）    PDF（pc） （6205KB）（520）       Knowledge map    Save Pyroclastic rock is the most direct object of physical volcanology and the most important topic of identifying the volcanic explosive fragmentation processes. Some particular species of pyroclastic rocks and equivalents can indicate key characteristics of the volcanism process, which is the basis to estimate the eruptive risks. Volcanic hazard is potential risk related to volcanic eruption, and it is one of the most important types of disasters that human beings face in nature. Volcanic disasters are directly related to the types of volcanic eruptions, among which explosive volcanic eruptions can cause the deadly intensive volcanic risks. The direct product of explosive volcanic eruption is to form various pyroclastic rocks, which represent the different types and intensities of volcanic hazards caused by the eruption process. The primary pyroclasts and secondary fragments reflect the difference of volcanic surface processes during eruptive or intermittent periods, while the distinguish of magmatic, phreatomagmatic and phreatic eruptive deposits marks the systematic development of modern volcanology, which is the leading work in the study of volcanic hazards. 1)Pyroclastic rocks are formed directly by transporting, accumulating and diagenesis of the expelled materials during the eruption. They usually consist of the primary materials such as broken magma, accidental fragments trapped by the volcanic conduit, as well as the epiclasts captured by the volcanic fluid flowing on the surface. Pyroclastic rock, as a direct product of explosive volcanism, has naturally becomes the most important research object in volcanology. The volcanic tephra laminae preserved by fine airfall volcanic ash in basins has been attracted attention because of their good isochron and environmental indication, and the associated rocks may need to be distinguished from different types of volcanic sedimentation such as bedded tuff, sedimentary tuff and tuffaceous mudstone. The autoclastic breccia produced by lava emplacement and the hyaloclatite formed by the quenching of lava under water represent fragmentation that is closely related to the lava flow, rather than those from explosive volcanism. 2)Pyroclast is mainly the product of explosive volcanism, but it can contain a certain amount of normal sedimentation and a small amount of rock fragment near the volcanic channel and the magma chamber roof. Pyroclats are generally defined as the direct products of explosive eruption behavior, while volcaniclastics are formed by volcanic degradation such as slope displacement, avalanche, lahar, and the autoclast generated by lava flowage and quenching. This classification not only emphasizes the difference in the forming process of different volcanic products, but also helps to distinguish the different mechanism in volcanological research and hazard estimation. Different types of pyroclastic rocks are formed with different fragment mechanisms and diagenetic ways, and some specific pyroclastic rocks represent various special types and scales of volcanic hazards. Although they are usually classified as primary clastics, the hazard caused by autoclastic breccia is significantly different. Cryptoexplosive breccia, although we have employed a rock name from pyroclastic rocks, is actually more concerned with its resource economics. 3)When we study the genetic types of pyroclastic rocks, the most important basis for identification is the forming mode of the materials, that is, the type of fragmentation, which include primary volcanism and secondary volcanism. Primary clasts are divided into pyroclast, which is formed by the direct action of volcanic eruption, and autoclast, which is produced by the flow process of lava flows, While secondary(exogenous)volcanism includes various kinds of exogenous clasts(epiclast)formed by volcanic surface processes. According to the proportion of magma and water content at eruptive environment, explosive eruption can be divided into three types: magmatic eruption, phreatomagmatic eruption and phreatic eruption, which represent the most basic process of explosive eruption, and are also the problems of genetic classification and identification often faced in the study of pyroclastic rocks. Table and Figures | Reference | Related Articles | Metrics

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INTEGRATED INTERPRETATION ON THE PRECURSORY PROCESS EVOLUTION IN THE META-INSTABILITY STAGE OF THE EARTHQUAKE: A CASE STUDY ON 2014 LUDIAN MS6.5 EARTHQUAKE JIANG Hai-kun, DENG Shi-guang, YAO Qi, SONG Jin, WANG Jin-hong SEISMOLOGY AND GEOLOGY    2024, 46 (3): 513-535.   DOI: 10.3969/j.issn.0253-4967.2024.03.001 Abstract （424）   HTML （44）    PDF（pc） （5232KB）（507）       Knowledge map    Save The transition from the metastable state to the meta-instability stage indicates that the seismic fault has entered an irreversible deformation process and will lead to an inevitable instability(Ma Jin et al., 2014). Therefore, identifying the meta-instability stage is helpful for the judgment of short-term earthquake precursor anomalies. Under laboratory conditions, the meta-instability stage can be visually identified through stress-time curves, thus potentially predicting the occurrence of the laboratory earthquake. However, there are significant differences between field conditions and laboratory environments. Firstly, the underground medium and structural conditions in the real earthquake source region are unclear and far more complex than laboratory specimens. Secondly, the distribution of the sensors, sensor density, as well as measurement accuracy are limited by various conditions, making it impossible to construct an ideal observation environment covering the entire region. Thirdly, the loading stress cannot be directly measured, and the current actual stress state of the study area is unknown, which is the most difficult problem to solve. Therefore, under the guidance of meta-instability experiments and theories, it is a beneficial attempt to conduct retrospective studies on typical earthquake cases with relatively good observation conditions in the past, analyze the spatial-temporal evolution of different physical fields at different stages before the earthquakes, compare the observed phenomena with the characteristics and change processes of meta-instability stages obtained from experiments or theoretical research. Its final goal is to find possible characteristics or indirect criteria for meta-instability stages under field observation conditions. Therefore, taking the Ludian MS6.5 earthquake as an example and under the guidance of the meta-instability experiments and theories, the paper comprehensively analyzes the relationship between the spatial-temporal evolution of precursory anomalies and the meta-instability process based on the seismic activity and the geophysical observation data prior the earthquake, and combined with numerical simulation results of the earthquake nucleation. The Ludian MS6.5 earthquake occurred on August 3, 2014 in northeastern Yunnan Province, China. The observation conditions in this region were relatively good, with 26 seismometers within a 300-km radius of the epicenter, which were able to basically monitor earthquakes with completeness magnitude ML≥1.5 and locating accuracy of less than 20km. There were 79 fixed geophysical observation stations, including 11 within 100km, 32 between 101~200km, and 36 between 201~300km. The observation terms covered 43 deformation observations(22 tilt observations, 18 borehole strain observations, and 3 gravity observations), 187 underground fluid observations(90 water physical observations such as water level and temperature, 43 material compositions measurements including radon, mercury and so on, 26 gas measurements such as CO2, and 28 ion measurements including bicarbonate, calcium, and magnesium), and 52 electromagnetic observations(36 geomagnetic observations, 16 resistivity and electromagnetic wave observations). There were a large number of credible medium- and short-term precursor anomalies before the Ludian MS6.4 earthquake, a total of 48 precursor anomalies were identified. Among of them, there were 8 seismic anomalies and 40 geophysical anomalies, accounting for approximately 15% of all measurement items. Among these 40 geophysical anomalies, 31 were proposed before the earthquake, and most of them were investigated and verified on-site with reliable changes.(Wu, et al., 2019). Based on this abundant precursor abnormally data before the Ludian MS6.4 earthquake and further systematic analysis, a typical earthquake case and relevant observational facts have been provided which can support the viewpoint that during the meta-instability stage, the earthquake nucleation occurred in the epicenter region and the synergy process evolved continuously in surrounding area of the epicenter. The results show that based on large-scale strong earthquake activities and the observation data of the mobile gravity, it can be determined that the concerned area was already in a high-stress state before the Luding earthquake. At that time, the stress level in the large area including the epicenter of the Ludian earthquake was relatively high, and the northeastern Yunnan region and its nearby areas where the Ludian earthquake occurred were already in a critical stress state where strong earthquakes could occur at any time. Under the premise of determining a high-stress state, according to the precursors of seismic activities and geophysical observation precursor anomalies, it can be roughly determined that the meta-instability process of the Ludian earthquake may have begun seven or eight months before the mainshock. The most prominent phenomenon or judgment index is the transition of the fault stress state from accumulation to release, characterized by the active of small earthquakes near the epicenter, as well as the synergistic phenomenon of fault deformation characterized by the significant increase in the number of geophysical observation anomalies, which is related to the expansion process of the core weakening zone in the late period of the earthquake nucleation. After that, until the occurrence of the mainshock, two times should be paying attention to. Firstly, four to five months before the mainshock, the spatial distribution range of the geophysical observation anomalies expands significantly from the epicenter area to the periphery region, indicating accelerated synergistic deformation of the fault. Secondly, after two months before the mainshock, the small earthquake activities near the epicenter began to weaken, and the micro-earthquake activities and the geophysical anomalies showed a migration and contraction towards the epicenter, which is associated with the contraction process of the core weakening zone during the final stage of the earthquake nucleation. The concept of seismic meta-instability proposed from the perspective of stress changes in seismic fault has an explicit physical implication, and the meta-instability stage is associated with the earthquake nucleation process(He et al., 2023). The basic premise for the meta-instability theory to play a role in short-term earthquake prediction lies in how to apply laboratory research results to natural earthquakes, understand whether the regional or fault stress state tends to or enters a meta-instability state through field observations, and further utilize it for practical earthquake prediction. 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RESEARCH PROGRESS AND APPLICATION OF CARBONATE U-TH/HE ISOTOPE DATING LI Yi-shan, LIU Hong, SUN Feng-xia, LIU Lei SEISMOLOGY AND GEOLOGY    2024, 46 (3): 723-738.   DOI: 10.3969/j.issn.0253-4967.2024.03.012 Abstract （509）   HTML （5）    PDF（pc） （1272KB）（485）       Knowledge map    Save U-series dating(Uranium series disequilibrium dating)is one of the most widely used dating methods in radioisotope geochronology, mainly based on the disequilibrium relationship between radionuclide 238U and its decay daughters 235U/234U and 230Th to measure the age of rocks, minerals, and other geological bodies. U-Th /He isotope dating is based on the decay of radioactive elements such as U and Th in mineral particles to form stable 4He isotopes. By measuring the cumulative content of these radioactive element decay products, The U-Th/He dating method has a large applicable time range for many minerals(such as apatite and zircon)and most geological periods, and can be used as a thermal timer to explain the thermal history of rocks, and can also be used as a geological timer to constrain the crystallization age of minerals and different geological events. Carbonate minerals, including calcite, dolomite, magnesite and aragonite, are widely distributed in the earth’s crust and formed in the processes of sedimentation, magma, metamorphism and hydrothermal fluid metasomatism. In recent years, with the development of closing temperature theory, the recognition of He diffusion behavior, and new progress in He measurement technique, it has been found that helium can be retained in the lattice of carbonate minerals, and the diffusion activation energy and low closure temperature are close to those of apatite. Carbonate U-Th/He isotope dating technology has been greatly developed and applied in the fields of geochronology and thermochronology, which attracted wide attention in the field of geology. Due to the large particle size and extremely low closure temperature, the application of low-temperature dating of carbonate minerals has received increasing attention. Ideally, a mineral crystal dating with U-TH /He should contain all helium from the decay of the U and Th radioisotopes inside the mineral, that is, there is no inheritance of previously existing helium, and there is no loss of helium after. Any factor that breaks the closure of the U-Th/He dating system will affect the accuracy of the dating results. Helium has a small atomic mass and no charge, and when the temperature is high enough, it easily diffuses out of the mineral lattice. This article mainly analyzes the influencing factors of He diffusion behavior and the new progress of He gas extraction and measurement technology. The study of the diffusion behavior of helium in carbonates is a key theoretical link in the development and application of U-TH/He dating methods for carbonates. Research methods, diffusion domain, crystal size, alpha particle and grain boundaries have different degrees of influence on helium diffusion behavior and helium retention. Accurate activation energy and diffusion coefficient of helium diffusion are needed to understand the mineral age of carbonates under certain geological conditions. The development of extraction and measurement technology for He gas is a key technical link in carbonate U-Th/He dating. Due to the low content of He, U and Th in carbonate samples, relatively large samples and advanced He measurement equipment such as vacuum furnaces and mass spectrometers are required. In-situ laser U-Th/He isotope dating, which has the advantages of high precision and non-destructive, has made a breakthrough in measuring carbonate ages and has gradually established a standard experimental testing process. Carbonate U-Th/He isotope dating technology has broad application prospects and research value in archaeology, brittle structure, oil and gas accumulation, oceanic crust evolution, metallogenic mechanism, and ore-forming fluid tracing, and will play an important role in solving earth science problems. In this paper, the progress of methods and techniques for carbonate U-Th/He dating in the last two decades is reviewed, the methods and basic principles of U-Th/He dating are summarized, the uncertainties affecting helium dating are analyzed, and the future development direction prospects. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE SEISMOGENIC STRUCTURE OF THE 2022 GUJIAO ML4.1 EARTHQUAKE IN SHANXI PROVINCE BASED ON FOCAL MECHANISM AND SEISMIC LOCATION DONG Chun-li, ZHANG Guang-wei, LI Xin-wei, WANG Yue-jie, DING Da-ye, GONG Zhuo-hong SEISMOLOGY AND GEOLOGY    2024, 46 (2): 414-432.   DOI: 10.3969/j.issn.0253-4967.2024.02.010 Abstract （476）   HTML （20）    PDF（pc） （4880KB）（477）       Knowledge map    Save Understanding the mechanism of earthquake sequence in the mining area is important for the time-dependent hazard assessment. An earthquake of ML4.1 occurred in Gujiao, Taiyuan, Shanxi on February 20th, 2022, which caused strong ground motion in Gujiao and surrounding counties. The epicenter of this earthquake is located in the area of Lvliang uplift, where historical earthquakes are relatively rare. In addition, the coal resources are well developed in the earthquake source area which has attracted much attention from society and local governments. To investigate the mechanism and the seismogenic fault of Gujiao ML4.1 earthquake, we first apply the double-difference location method to retrieve highly accurate hypocenter locations. The results show that the earthquakes mainly occur at a depth range of 3~5km, and display a dominant distribution direction nearly EW-trending, which differs significantly from the NE-trending fault distribution pattern in this region. We further collect the broad-band seismic waveforms from the regional network of Shanxi province to perform focal mechanism inversion. The inversion results show that the Gujiao earthquake is a left-slip seismic event with a moment magnitude of MW3.96. The optimal double-couple solution is characterized by a strike of 90°, dip of 80°, and a rake angle of -21° for fault plane Ⅰ, while for the fault plane Ⅱ, the strike is 184°, dip is 69°, and rake angle is -169°. The best centroid depth is estimated to be at 3km. This earthquake shows an extremely shallow focal depth. Moreover, By using cluster analysis method, we obtained the central solution for the seismogenic fault plane of the GuJiao earthquake, with a fault strike of 91°and a dip angle of 70°. The focal solutions show that the earthquake exhibit a strike-slip type, and the orientations of earthquake sequence coincide well with the focal mechanisms. In addition, to discuss the effect of Gujiao ML4.1 earthquake on regional stress, we calculate the stress drop of this seismic sequence. The results show that the stress drop is significantly smaller than that of the regional earthquakes, exhibiting at least one order of magnitude lower than that of the background earthquakes in the same region. This phenomenon reflects that the stress level in the focal area of the GuJiao earthquake is not high, suggesting that the background stress enhancement in the focal area is not obvious. Based on regional geological structure, we found that the known faults in the region are all high-angle normal faults, and the strike of these faults are inconsistent with the focal mechanism solution of Gujiao earthquake sequence, which suggests that the existing faults are not the seismogenic fault. Taking the regional mining activities into account, we speculated that mining may cause strong disturbance to the stress field, and lead to stress redistribution within the rock mass. Such coal mining activity may generate a high stress disturbance on the hidden fault plane, and then the fault become the carrier of stress transfer. So we conclude that the seismogenic mechanism of the Gujiao-seismic sequence may be related to coal mining activities near the focal area, which leads to local stress changes, thus resulting in the activation of preexisting hidden faults and triggering the occurrence of the Gujiao earthquake. Table and Figures | Reference | Related Articles | Metrics

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DEVELOPMENT AND PROSPECT OF THERMOLUMINESCENCE DATING BY USING CALCITE QIN Ke-xin, HU Gui-ming, LIU-ZENG Jing, SHEN Xu-wen, GAO Yun-peng, WANG Wen-xin, WEN Xin-yu, JIANG Shuai-yu SEISMOLOGY AND GEOLOGY    2024, 46 (3): 699-722.   DOI: 10.3969/j.issn.0253-4967.2024.03.011 Abstract （470）   HTML （13）    PDF（pc） （3484KB）（459）       Knowledge map    Save The accumulation of luminescence signals in mineral crystals correlates with the duration of exposure to radiation. This phenomenon has been utilized as a tool for measuring sediment age and has found extensive application in various research endeavors. While quartz and feldspar luminescence signals have been utilized for dating in recent years, their effectiveness is constrained by early saturation, limiting their dating range to less than 300ka. In contrast, calcite exhibits high sensitivity to dose responses of thermoluminescence signals and possesses a characteristic saturation dose that can reach levels of 3 000-5 000Gy, making it a promising material for thermoluminescence dating. This has the potential to extend the age range of luminescence dating to the Quaternary period and broaden the application scope of low-temperature thermochronology. Providing quantitative descriptions of bedrock exhumation history through low-temperature thermochronology can offer crucial data support for understanding the interconnected relationship between tectonic activity, climate influences, and geomorphic evolution. Low-temperature thermoluminescence thermochronology, characterized by its high resolution and low closure temperature, presents advantages over commonly used apatite U-Th/He thermochronology in elucidating the excavation history of the Earth’s crust surface(approximately 1~2km). However, traditional minerals utilized for reconstructing bedrock cooling history, such as quartz and feldspar, exhibit rapid saturation, limiting the study period to less than 200ka. In contrast, calcite boasts an exceptionally high characteristic saturation dose and lower dose rate, making it a promising new dating mineral that extends the upper limit of low-temperature thermoluminescence thermochronology beyond 0.5Ma. This paper begins by introducing the principle and application of thermoluminescence dating, followed by an overview of commonly used techniques for measuring dose rate and equivalent dose. The thermoluminescence dating process primarily involves equivalent dose measurement and dose rate measurement. Considerable research has been conducted on equivalent dose, and newly developed methods such as single aliquot regenerative dose, multiple aliquot regenerative dose, and multiple aliquot-additive dose have addressed issues related to sensitivity changes caused by heating, thereby enhancing the accuracy of dating results. Additionally, the paper summarizes recent advancements in calcite thermoluminescence dating and kinetic parameters. To validate the method, we performed thermoluminescence dating analysis on calcite grains in bedrock samples collected from the Tiger Leap Gorge of the Jinsha river. After passing through Shigu, the Jinsha river experiences a sudden change in flow direction, carving its way through the Yulong-Haba mountain range to create the renowned “Tiger Leaping Gorge.” This geographic feature is characterized by active tectonics and intense river erosion, making it an ideal site for investigating the interplay among tectonics, climate, and surface processes. However, the Tiger Leaping Gorge primarily comprises limestone and griotte, lacking minerals such as apatite and zircon necessary for traditional low-temperature thermochronology dating(only exposed in the Upper Tiger Leaping Gorge). Consequently, it presents an ideal setting for exploring calcite low-temperature thermoluminescence thermochronology. SAR-ITL can detect the 280℃ thermoluminescence peak signal of calcite at 235℃, effectively mitigating the influence of spurious thermoluminescence. Moreover, the number of calcite grains required is lower than that of the MAAD test. The findings highlight the potential of this method for estimating the exhumation rate of carbonate rock. To facilitate its more effective utilization in the field of tectonic geomorphology, we address the challenges and potential applications of calcite thermoluminescence dating. Table and Figures | Reference | Related Articles | Metrics

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APPLICATIONS AND ADVANCES FOR THE COSEISMIC DEFORMA-TION OBSERVATIONS, EARTHQUAKE EMERGENCY RESPONSE AND SEISMOGENIC STRUCTURE INVESTIGATION USING INSAR ZHAO De-zheng, QU Chun-yan, ZHANG Gui-fang, GONG Wen-yu, SHAN Xin-jian, ZHU Chuan-hua, ZHANG Guo-hong, SONG Xiao-gang SEISMOLOGY AND GEOLOGY    2023, 45 (2): 570-592.   DOI: 10.3969/j.issn.0253-4967.2023.02.016 Abstract （936）   HTML （41）    PDF（pc） （7303KB）（446）       Knowledge map    Save With the recent development of geodetic observation theory, the increasing satellite platforms and the progress of related technology, InSAR is emerging as a new data source and useful tool for remotely-based geodetic observations. More importantly, InSAR observations play an increasingly irreplaceable role in the field of coseismic deformation observations, earthquake emergency responses, earthquake hazard evaluation and seismogenic structure research. Particularly, InSAR is the most commonly used tool in coseismic deformation measurements on the Qinghai-Tibetan plateau or other global seismic zones, where GPS data are sparse or inaccessible in some cases. Specifically, InSAR measurements help us to respond in time after disastrous earthquakes and provide valuable information associated with how the surface of the crust deforms due to large earthquakes. In the area of scientific research, InSAR provides products of surface deformation observations and serves as model constraints kinematically or dynamically in identifying the buried faults, studying the characteristics of seismogenic faults, obtaining three-dimensional displacements, and investigating the relationship between earthquakes and tectonic structures. InSAR observations and its deformation products have the technical advantages of large spatial scale, high precision and in-time, compared to other geodetic measurements. Consequently, InSAR has the ability to provide scientific and technological support for earthquake emergency observations, and meeting the practical needs of earthquake disaster reduction on the Qinghai-Tibetan plateau. In this review, we mostly limit our focus to the application of InSAR technology in earthquake cycle deformation monitoring in different structural settings on the Qinghai-Tibetan plateau. We also summarize the InSAR-based studies on fault kinematics and seismogenic structures related to some noted earthquakes on the Qinghai-Tibetan plateau. We highlight how the applications of InSAR data can greatly promote earthquake science and can be used as routine observations in some important areas. Then proceed to discuss the cutting-edge development trend and some new challenges of InSAR technology, which are frequently discussed and investigated, but not well resolved, in recent applications. The endeavors in increasing the precision of small-magnitude deformation measurements and expanding the InSAR data volumes can make the scientific objectives of earthquake disaster reduction on the Qinghai-Tibetan plateau and its surrounding areas feasible and reliable. To better understand how InSAR observations have changed the way we study earthquakes, we summarize the development, commercialization, insights, and existing challenges associated with InSAR coseismic deformation measurements and application in recent two decades. Table and Figures | Reference | Related Articles | Metrics

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SURFACE RUPTURE INTERPRETATION AND BUILDING DAMAGE ASSESSMENT OF XIZANG DINGRI MS6.8 EARTHQUAKE ON JANUARY 7, 2025 ZOU Jun-jie, SHAO Zhi-gang, HE Hong-lin, GAO Lu, XU Yue-yi, DOU Ai-xia, LIANG Ze-yu SEISMOLOGY AND GEOLOGY    2025, 47 (1): 16-35.   DOI: 10.3969/j.issn.0253-4967.2025.01.002 Abstract （732）   HTML （31）    PDF（pc） （18854KB）（410）       Knowledge map    Save On January 7, 2025, at 9:05 AM, a 6.8-magnitude earthquake struck Dingri County, Shigatse City, Xizang, at a depth of 10km. The maximum intensity of the earthquake reached Ⅺ degrees. This study provides a comparative analysis of pre- and post-earthquake remote sensing images using GF-2 satellite data. The results identify the Dengmecuo fault as the primary seismogenic fault for the earthquake. Surface ruptures exhibit distinct geometric variations between the northern and southern segments. The northern segment, approximately 3km in length, features a relatively simple geometry with a narrow rupture width, forming a “concentrated rupture” pattern characterized by continuity. In contrast, the southern segment, approximately 12km long, displays a more complex geometry with a wider rupture width, resulting in a “diffuse rupture” pattern marked by discontinuities. Statistical analysis of building collapses and damage in 28 administrative villages near the epicenter shows that the severity of impact follows this order: Changcuo township, Cuoguo township, and Quluo township. Affected villages were classified based on their geological and geographical conditions, revealing that the earthquake's impact diminished in the following sequence: areas near the micro-epicenter, lake regions adjacent to the surface rupture zone, and bedrock mountainous areas far from the epicenter and rupture. Coseismic surface rupture analysis reveals two fault segments near Dengmecuo Lake that did not rupture. Considering the unilateral rupture pattern from south to north and the distribution of aftershocks, it is suggested that the unruptured southern segment may pose a greater seismic hazard. At a regional scale, normal faults within the fault system, including the Quluo, Dengmecuo, Guojia, and Dingjie faults, all exhibit aftershock activity. Given the recent release patterns of moderate-to-strong earthquakes, special attention should be given to the seismic risk associated with the Quluo and Dingjie faults. Finally, based on the geographical conditions, seismogenic structures, and seismic damage patterns, this study offers strategies for mitigating seismic risks in high-altitude, high-latitude regions with diverse geological and geomorphological features, diffuse fault deformation patterns, and populations of ethnic minorities. Table and Figures | Reference | Related Articles | Metrics

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THE 2022 M6.8 LUDING EARTHQUAKE: A COMPLICATED EVENT BY FAULTING OF THE MOXI SEGMENT OF THE XIANSHUIHE FAULT ZONE LI Chuan-you, SUN Kai, MA Jun, LI Jun-jie, LIANG Ming-jian, FANG Li-hua SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1648-1666.   DOI: 10.3969/j.issn.0253-4967.2022.06.017 Abstract （1177）   HTML （94）    PDF（pc） （16086KB）（397）       Knowledge map    Save The September 5, 2022, M6.8 Luding earthquake occurred along the southeastern segment of the Xianshuihe fault zone. Tectonics around the epicenter area is complicated and several faults had been recognized. Focal mechanisms of the main shock and inversions from earthquake data suggest that the earthquake occurred on a northwest-trending, steeply dipping strike-slip fault, which is consistent with the strike and slip of the Xianshuihe fault zone. We conducted a field investigation along the fault sections on both sides of the epicenter immediately after the earthquake. NW-trending fractures that were recognized as surface ruptures during the earthquake, and heavy landslides along the fault section between Ertaizi-Aiguocun village were observed during the field investigations. There are no surface ruptures developed along the fault sections north of the epicenter and south of Aiguocun village. Thus it can be concluded that there is a 15.5km-long surface rupture zone developed along the Moxi Fault(the section between Ertaizi and Aiguo village). The surface rupture zone trends northwest and shows a left-lateral strike slip, which is consistent with the strike and motion constrained by the focal mechanism. The coseismic displacements were measured to 20~30cm. Field observations, focal fault plane, distribution of the aftershocks, GNSS, and InSAR observation data suggest that the seismogenic structure associated with the M6.8 Luding earthquake is the Moxi Fault that belongs to the southeastern segment of the Xianshuihe fault zone. Slip along the segment south of the epicenter generated this earthquake, and also triggered slip along a northeast-trending fault and the northwestern section of the Moxi Fault in the epicenter. So, the M6.8 Luding earthquake is an event that is nucleated on the section south of the epicenter and then triggered an activity of the whole fault segment. Table and Figures | Reference | Related Articles | Metrics

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THE CHARACTERISTICS AND MECHANISM OF FLUID ANOMALIES IN THE DAZHAI OBSERVATION WELL OF PU’ER, YUNNAN PROVINCE BEFORE THE M5.9 MOJIANG EARTHQUAKE ON SEPTEMBER 8, 2018 HU Xiao-jing, FU Hong, ZHANG Xiang, LI Li-bo, HUANG Jiang-pei, LI Qiong, GAO Wen-fei SEISMOLOGY AND GEOLOGY    2024, 46 (2): 477-491.   DOI: 10.3969/j.issn.0253-4967.2024.02.014 Abstract （366）   HTML （14）    PDF（pc） （6351KB）（394）       Knowledge map    Save The precursors before earthquakes are very useful to earthquake prediction, and fluid anomalies before earthquakes are very important to precursory observations. This paper reviews the characteristics of hydrochemical ions and well-aquifer permeability anomalies of the Dazhai observation Well in Pu’er, which is in the Yunnan-Southwestern region of China, for all M≥5.5 earthquakes since 2004. We find that both the chemical ions and physical parameters before the Mojiang M5.9 earthquake exhibited the largest magnitude of changes since observation, and the abnormal state was much stronger than that of previous historical earthquakes, but the magnitude of the earthquake was below 6. About 1.5-2a before the M5.9 Mojiang earthquake, the composition of hydrogen and oxygen isotopes of the water samples in the Dazhai observation Well showed a significant deviation, accompanied by a continuously increasing concentration of fluoride ions from sources at deeper depths. This might suggest that the deep material in the earthquake source area began to be active. At the same time, starting one year before the earthquake, the phase lag of the water level in the wellhole changed from negative to positive, indicating that the source and pathway of well water recharge have been changed. In addition, around half a year before the earthquake, the continuously observed water chemical ions at shallow depths in the wellhole began to show a dramatic change. Moreover, macroscopic anomalies of hot spring water volume increased sharply before the earthquake, showing a remarkable evolution process from deep to shallow, from background to short-term, and from micro anomalies to macro anomalies before the earthquake. To investigate the causes and mechanisms of this phenomenon, we attempt to discuss the abnormal evolution process before the M5.9 Mojiang earthquake from the aspects of regional deep material activity and regional stress level. The abnormal concentration of the hydrochemical ions and the change of aquifer permeability observed continuously at the Dazhai observation well before the M5.9 Mojiang earthquake were caused by the continuous increase in shear stress in the region, which caused the aquifer to be compressed, resulting in a vertical fluid recharge and ultimately the alternation and mixing of different aquifer water bodies. In addition to being controlled by the continuous increase in regional vertical shear stress, the abnormal formation process was also accompanied by the intense activity of deep-sourced chemical elements such as helium isotope and fluoride ion. The abnormal evolution process showed a remarkably coupled process of migration from deep to shallow, which may be the reason why the shallow ion anomaly before the M5.9 Mojiang earthquake was the most significant among all the observed cases. Therefore, the evolution process of fluid activity starting from the deep and continuously transmitting to the surface with the accumulation of regional stress is essential to the abnormal evolution of the hydrological phenomenon before the M5.9 Mojiang earthquake. The regional stress and the process of deep material activity are the biggest differences between the M5.9 Mojiang earthquake and other historical earthquake cases in the study area, which will be the two main factors to be considered when similar ion changes occur again in the future. Our study provides insight into a comprehensive understanding of the predictive significance of underground fluid anomalies in the Dazhai well and the coupled evolution process of deep-shallow fluid anomalies before the earthquake. Table and Figures | Reference | Related Articles | Metrics

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GEOCHEMICAL CHARACTERISTICS AND GENESIS OF SOIL GAS IN THE PINGYUAN M5.5 EARTHQUAKE SU Shu-juan, CHEN Qi-feng, SUN Hao, LIU Jun, FENG Liang-le, XU Ji-long, YANG Yan-ming, LUO Kun-li SEISMOLOGY AND GEOLOGY    2024, 46 (2): 433-448.   DOI: 10.3969/j.issn.0253-4967.2024.02.011 Abstract （413）   HTML （20）    PDF（pc） （7314KB）（373）       Knowledge map    Save At 2:33 am on August 6, 2023, a M5.5 earthquake occurred in Pingyuan county, Dezhou city, Shandong Province. The faults within the epicenter and adjacent areas are deeply buried by the thick Quaternary sediment cover on which human activity is intensive, which makes it difficult to determine the location of the buried active faults from the surface based on geological and geomorphological evidences. It is necessary to detect the location of the buried active faults around earthquake areas and estimate their seismic risk. In this study, based on the epicenter distribution direction of major earthquake and aftershocks, seismic and geological data of earthquake areas, and damage degree of local buildings, 4 survey lines with a length of 30km were arranged across the epicenters and adjacent areas, and the concentrations of Rn, CO2 and Hg in soil gas were measured on site, and the results are as follows: (1)There are obvious spatial differences in the concentrations of soil gas near the epicenter and its vicinities within the distance of 30km. Gas concentrations are relatively high near the epicenter areas and the east and west ends of 4 arranged survey lines, in contrast to those which are relatively low in other non-structural control regions. The spatial distribution pattern of Rn concentration in soil gas is basically consistent with that of CO2, which may be due to CO2 used as a carrier gas of Rn to migrate to the surface. At the southern end of the Lingxian-Guanxian Fault(F1), the spatial concentration patterns of Rn and CO2 gases exhibit multiple peaks or wide anomalous zones. It is speculated that the deformation zone of the fault rupture at this location is relatively wide, and there may be secondary permeable fracture zones in the west of the F1. The escape form of Rn and CO2 gas indicates that there may indeed be multiple small fault branches near the F1, and the fault structure is relatively complex. (2)The spatial concentration distributions of Hg, Rn and CO2 in the epicenter areas are similar to that in its eastern region. However, in the western region of the epicenter areas, the spatial concentration distributions of Hg, Rn and CO2 vary greatly, and the Rn and CO2 concentrations near the Jiucheng Fault(F3) in the west of the epicenter regions are higher than those near epicenters. It is speculated that this phenomenon may be related to the high-concentration gas migration caused by strong seismic tectonic activities and the special nasal geological structure controlled by F3. (3)The concentrations of Rn, CO2 and Hg in the soil show high-value anomaly zones near the F1 and F3, and the concentrations of Rn and CO2 in the west of F3 exceed those in the epicenter area. After further earthquake relocation analysis, the spatial distribution of aftershocks exhibit a trend from F1 to F3. Combined with geochemical and geophysical research results, it is inferred that Pingyuan M5.5 earthquake should be related to the deep tectonic activities of F1 and F3. Above research results show that the soil gas geochemical method can be applied to define the location and distribution direction of the buried faults with thick overburden, which provides an important criterion for earthquake trend tracking analysis. This study is of greatly scientific significance in determining the dynamic source and genetic mechanism of Pingyuan M5.5 earthquake, identifying potential strong earthquake hazard areas, and assessing the risk of future earthquakes in the study area. Table and Figures | Reference | Related Articles | Metrics

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CHARACTERISTICS OF FOCAL MECHANISM AND STRESS FIELD IN THE EASTERN BOUNDARY OF THE SICHUAN-YUNNAN BLOCK GUO Xiang-yun, FANG Li-hua, HAN Li-bo, LI Zhen-yue, LI Chun-lai, SU Shan SEISMOLOGY AND GEOLOGY    2024, 46 (2): 371-396.   DOI: 10.3969/j.issn.0253-4967.2024.02.008 Abstract （622）   HTML （26）    PDF（pc） （11846KB）（373）       Knowledge map    Save It is important to study the characteristics of the tectonic stress field studies which could provide a deeper understanding of the internal stress environment of the crust. It can provide useful assistance for exploring the relationship between the tectonic stress field and earthquake development. At the same time, it plays an important role in understanding block interactions, fault movement, tectonic deformation, and revealing the dynamic mechanical processes of the continent. The focal mechanism solutions contain abundant information reflecting the stress field. In this paper, using the broadband records from 128 permanent and temporary regional stations from the Chinese National Seismic Network(CNSN)deployed in the Sichuan-Yunnan Province and its adjacent, we determined the focal mechanisms of 3 951 earthquakes by the cut-and-paste(CAP)method and the HASH method. The friction coefficient and stress properties of the main active fault and characteristics of the tectonic stress field in this area are analyzed by using two different methods which are the damped inversion method(STASI)and iterative joint inversion method from focal mechanisms. The results of the focal mechanisms show that: there are 2 512 strike-slip earthquakes in the study area, accounting for 63.58% of all earthquakes; there are 818 normal fault type and normal strike-slip type earthquakes, accounting for 20.70% of all earthquakes; there are 621 reverse strike slip and reverse thrust earthquakes, accounting for 15.72% of all earthquakes. The most of earthquakes in the study area are distributed in active fault zones, the strike of the fault plane is consistent with the orientation of active fault zones. It revealed predominantly strike-slip faulting characteristics of earthquakes in the Eastern Boundary of the Sichuan-Yunnan Block, while the reverse thrust of earthquakes is mainly concentrated in the Longmenshan fault zone, as well as the NW trending Mabian-Yanjin Fault and the NE trending of Ludian-Zhaotong and Lianfeng faults which lied on the eastern boundary of the Sichuan-Yunnan block. Overall, the characteristics of the source mechanism are consistent with the regional tectonic background. Results of the stress field inversion confirmed main active fault in the Eastern Boundary of the Sichuan-Yunnan Block is under a strike-slip stress regime, maximum and minimum compressional stress axes are nearly horizontal. The maximum compressional axes are primarily oriented in NW-SE and NWW-SEE direction, and they experience a clockwise rotation from north to south. Against the strike-slip background, normal faulting stress regimes and reverse faulting stress can be seen in the regional areas. The most prominent is the Daliangshan fault zone, which has obvious differences from the overall characteristics of the stress field with the eastern boundary of the Sichuan Yunnan Block. The maximum horizontal principal stress in the northern section shows a nearly EW direction, with a strike-slip type stress property, and the NW-SE direction in the southern section, with a thrust type stress property. The distribution characteristics of the stress field are consistent with the fault type of sinistral strike-slip and thrust on the eastern boundary of the Sichuan Yunnan block The shape ratio R-value varies significantly, the R-value in the Sanchakou area is relatively high, with obvious extrusion characteristics, the R-values of the Xianshuihe fault zone, Anninghe fault zone and Xiaojiang fault zone are all between 0.25-0.5, showing NE-SW compression and NW-SE tension, and the tensile stress may be much less than the compressive stress(strike-slip type). The R values of the northern segment of the Daliangshan fault zone, the southern segment of the Anninghe fault zone, and Zemuhe fault zone are all between 0.5-1, showing NW-SE compression and NE-SW tension, and the compressive stress is greater than the tensile stress. To sum up, the current stress characteristics of the eastern boundary of the Sichuan Yunnan rhombic block are shear strain and local compression or tension. There are different friction coefficients of the main faults in the study area: The Anninghe fault zone is 0.60, the Xianshuihe and Zemuhe fault zones are 0.80, the Xiaojiang fault zone is 0.75 and northern and southern sections of the Daliangshan fault zone are 0.65 and 0.85. The friction coefficients of the Xianshuihe Fault, the southern section of the Daliangshan Fault, and the Zemuhe Fault are above 0.75. The high friction coefficients of these fault zones may be because they are strike-slip faults, and the friction coefficients themselves are relatively high. The southern section of the Xiaojiang fault zone may be related to the development of fault gouges in the fault zone. Table and Figures | Reference | Related Articles | Metrics

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FINE CHARACTERISTICS OF EARTHQUAKE SURFACE RUPTURE ZONE BASED ON HIGH-RESOLUTION REMOTE SENSING IMAGE: A CASE STUDY OF LITANG FAULT YOU Zi-cheng, BI Hai-yun, ZHENG Wen-jun, PENG Hui, LIANG Shu-min, DUAN Lei, QIN Yi-gen SEISMOLOGY AND GEOLOGY    2023, 45 (5): 1057-1073.   DOI: 10.3969/j.issn.0253-4967.2023.05.002 Abstract （563）   HTML （54）    PDF（pc） （10517KB）（365）       Knowledge map    Save Strong earthquakes(magnitude>6.5)typically cause coseismic surface ruptures of several kilometers or even hundreds of kilometers long on the surface. Coseismic surface rupture is the most intuitive geomorphic representation of an earthquake on the surface, and its geometry and distribution characteristics provide important information about the fault activity. Field investigation is the most basic means for research on coseismic surface fractures, but for areas that are hard to access or have harsh climatic environments, field investigation is often greatly limited. In recent years, the increasing abundance of high-resolution remote sensing images and the rapid development of photogrammetry methods can help us quickly obtain high-resolution topographic and geomorphic data of the study area, to better identify the fine geometry of the earthquake surface rupture zone and measure the offsets of geomorphic markers along the fault. The Litang Fault is a sinistral strike-slip fault located within the Sichuan-Yunnan rhombic block on the eastern edge of the Qinghai-Tibetan plateau. Several historical earthquake events have occurred on this fault, such as the 1890 and 1948 earthquakes, and clear seismic surface ruptures still exist along the fault so far. Previous studies have conducted a series of works on the coseismic surface rupture of this fault, but most of these works were based on field investigations or relatively low-resolution remote sensing images, and there is still a lack of fine research on the coseismic surface rupture of the fault. In this paper, the coseismic surface rupture of the 1890 earthquake which occurred on the Litang Fault was selected as the study object. To obtain high-resolution topographic data of this fault, the WorldView satellite stereo images were used to generate a 0.5-m-resolution orthophoto and a 1-m-resolution Digital Elevation Model(DEM)of the Litang fault based on the photogrammetry method. With the high-resolution topographic data, the fine geometry of the 1890 earthquake surface rupture zone was mapped in detail. The mapping results show that the total length of the surface rupture is about 27km, with an overall strike of N40°W. The rupture is mainly characterized by sinistral strike-slip motion, with a certain degree of dip-slip component in local areas. Except for the interval of approximately 6km with no surface rupture at the Wuliang River floodplain in the Litang Basin, the surface ruptures are relatively continuous at other locations. In addition, various rupture styles have been identified along the fault, including en echelon tension cracks, mole tracks, sag ponds, fault scarps, and displaced gullies. Furthermore, the sinistral offsets of 90 groups of linear geomorphic markers such as gullies and ridges were measured along the fault, which range from 1m to 82.4m. We further estimated the Cumulative Offset Probability Distribution(COPD)of the offsets located on the terrace I of the Wuliang River, which are all in the range of 0-9m. The COPD plot displays four distinct peaks at 1.3m, 2.4m, 4.3m, and6.1m, respectively. Previous studies have reported that the terrace I of Wuliang River formed at about(4 620±40)a BP. Thus, it can be indicated that the Litang fault may have experienced at least four strong earthquake events since(4 620±40)a BP, and the smallest peak of 1.3m may represent the coseismic displacement of the most recent 1890 earthquake. The rupture length of the latest 1890 earthquake was about 27km, and the coseismic sinistral offset was about 1.3m, yielding an estimated moment magnitude of MW6.8-7.1. The coseismic offset of the other three earthquakes was about 1.8m, 1.9m, and 1.1m from old to new, respectively, yielding a magnitude estimate of MW7.3, MW7.3, and MW7.0, with a size comparable to the 1890 earthquake. The research results fully demonstrate the potential of high-resolution remote sensing images in the study of fine characteristics of earthquake surface rupture. Table and Figures | Reference | Related Articles | Metrics

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SIMULATION OF THE ROCK SURFACE LUMINESCENCE SIGNALS ON BEDROCK FAULT SCARPS BY STICK-SLIP AND CREEP MOVEMENTS LUO Ming, CHEN Jie, QIN Jin-tang, YIN Jin-hui, YANG Hui-li, LIU Jin-feng, GONG Zhi-jun SEISMOLOGY AND GEOLOGY    2024, 46 (2): 357-370.   DOI: 10.3969/j.issn.0253-4967.2024.02.007 Abstract （424）   HTML （9）    PDF（pc） （3308KB）（359）       Knowledge map    Save The reconstruct of the stick-slip and creep histories is essential for understanding fault activities and seismic hazard assessment. Distinguishing stick-slip and creep using geodetic technology has become a hot research area in recent years, but distinguishing and estimating seismic slip and creep on geological timescales(e.g., over hundreds of years)is challenging due to the lack of historical, geodetic and remote sensing data extending back more than a few hundred years. This study uses a newly developed dating technique(rock surface optically-stimulated-luminescence(OSL)dating)combined with the OSL decay parameters of granite samples from the Langshan fault in Inner Mongolia to simulate optically stimulated OSL-depth curves and depths of half saturation of luminescence signal under various scenarios such as fault seismic slipping, creeping, and erosion of colluvial wedge. The study compares these OSL-depth profiles, especially the depths of the half saturation, under different slipping modes, and summarizes their features. During fault seismic slip, samples at different heights along the fault scarp display a “step-like” distribution pattern at their depths of half saturation. While during creep, however, they exhibit a “slope-like” pattern. Such differences may lie in that the slope during accelerating creeping is steeper than the slope during constant-speed creeping. Correspondingly, the resolution of residual luminescence-depth profile and depth of half saturation is also higher during accelerating creeping. During intra-earthquake creep events between seismic slip occurrences on the bedrock fault scarp, the distribution of half-saturation depth in the samples includes segments resembling both “steps” and “slopes”, which indicate the seismic slip and creep activities of the fault respectively. If the samples at the base of the colluvial wedge have had a sufficiently long last exposure time, the luminescence-depth profile and half-saturation depth distribution due to the erosion of the colluvial wedge would be approximately the same as in the three-phase seismic slip scenario. This indicates that samples previously buried by the colluvial wedge may be considered within the seismic displacement. Conversely, if the last exposure time of the base samples at the base of the colluvial wedge is short, the bleaching depth of the luminescence signal of these base samples will be noticeably shallower than that of the other samples within the seismic displacement, indicating the observed erosion of the colluvial wedge in this case. Furthermore, the seismic displacement ideally should include the buried location of the colluvial wedge. Therefore, when the luminescence curves and half-saturation depth distributions fail to identify the presence of the colluvial wedge, it is acceptable to include the buried location of the colluvial wedge in the seismic displacement calculation. Conversely, the luminescence-depth curves and half-saturation depth distributions document the erosion caused by the colluvial wedge. The simulation results demonstrate that this method can effectively distinguish between fault slipping and creeping, obtain corresponding displacements, and potentially record the erosion of colluvial wedge. This study also analyzes the temporal resolution of the method for distinguishing fault activity times and the spatial resolution for quantifying displacements. The specific situation is as follows. When exposure age of the bedrock fault scarp is within a thousand years, the rock surface OSL dating method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval of hundreds of years. When exposure age of the bedrock fault scarp is in the range of 100-101ka, the method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval exceeding a thousand years. When exposure age of the bedrock fault scarp is over ten-thousand years, the resolution of this method may be significantly reduced. The spatial resolution of seismic displacements using this method depends on interval between sampling and testing samples, typically in 10~30cm. Table and Figures | Reference | Related Articles | Metrics

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PALEOSEISMOLOGIC STUDY ON THE YUEXI FAULT IN THE MIDSECTION OF THE DALIANGSHAN FAULT ZONE SINCE THE LATE QUATERNARY LIU Qing, LIU Shao, ZHANG Shi-min SEISMOLOGY AND GEOLOGY    2023, 45 (2): 321-337.   DOI: 10.3969/j.issn.0253-4967.2023.02.002 Abstract （564）   HTML （55）    PDF（pc） （15181KB）（357）       Knowledge map    Save The Xianshuihe-Xiaojiang fault system(XXFS)is a strongly active left-lateral strike-slip fault zone on the eastern edge of the Qinghai-Tibetan plateau. It controls the eastern boundary of the Sichuan-Yunnan block, Which is one of the most active tectonic zones in the north-south seismic belts. There have been 36 destructive earthquakes since 1327AD. The historical strong earthquakes in the middle section of the XXFS fault system are mainly distributed along Anning River faults and Zemu River faults, such as M7.0 in 814AD, M71/2 in 1536AD, M63/4 in 1732AD, M71/2 in 1850AD and M63/4 earthquakes in 1952AD. However, as an important part of the middle of XXFS, the Daliangshan fault zone only recorded a magnitude of M51/2 in 1480AD, and there was a lack of earthquake records above a magnitude of 6 which may be due to the quiet period of earthquakes, or the location of remote mountainous areas where historical records are missing. The paleoseismic study revealed that there were surface rupture events along the Butuo and Jiaojihe faults in the southern section of the Daliangshan fault zone in 970-1510AD and 1310-1660AD respectively, with a magnitude of not less than 6.5; Along the Puxiong fault in the middle section of the Daliangshan fault zone, there was a surface rupture event in 927-1360AD, with a magnitude of not less than 7.0. However, there are no corresponding historical records of the earthquakes in these three historical periods, indicating that strong historic earthquakes in the Daliangshan fault zone may be missing. The Yuexi fault is the only branch fault in the Daliangshan fault zone dominated by thrust slip. The fault spreads in an arc shape, with a total length of about 50km, and controls the quaternary basins such as Zhenxi, Xinmin, and Yuexi. The topographic height difference between the fault’s two sides is about 2 000m. The middle section of the fault is the eastern boundary fault of the Yuexi Basin, which cuts through the piedmont alluvial fan, forming fault scarps several meters to tens of meters high. Together with the Puxiong fault on the east side, which is dominated by left laterally slipping, a positive flower-type structure is formed in the middle section of the Daliangshan fault zone. There are previous discoveries about fault scarps of the Yuexi fault on the piedmont alluvial fans, but no paleoseismic research has been reported up to now. On the basis of remote sensing interpretation and field geological and geomorphological survey of the Yuexi fault, a big trench was excavated across the 12m-high fault scarp on the late quaternary alluvial fan in the Yuexi Basin, which revealed four paleoseismic events since the late quaternary and the coseismic vertical slip of the last one is ~1.2m. Based on trench analysis, 14 stratigraphic units are defined from which carbon samples are acquired for geochronological analysis. Through radioactive carbon dating and correction of the dating data by the OxCal software, and OxCal model building to limit the age of paleoearthquake events, the ages of the four events were 25260-23880BC, 23930-23500BC, 20980-1400BC, and 270-1500AD. According to historical records, a destructive earthquake occurred in Yuexi County on September 13, 1480AD, which triggered landslides, 7 earthquakes on that day, and more than 20 aftershocks as of the 27th, with a tremor range of 150km. We consider that the latest event should be the Yuexi earthquake in 1480AD according to the historical records of earthquake damages. Based on the paleoearthquake research, this event very likely led to a coseismic rupture of the Yuexi and the Puxiong faults. According to the empirical scaling laws between magnitude and rupture length, the magnitude of the surface ruptured paleoearthquake is estimated to be more than M7.0. The results provide basic data for evaluating seismic activity and analyzing seismic risk in this area. Table and Figures | Reference | Related Articles | Metrics

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3D P-WAVE VELOCITY STRUCTURE OF CRUST IN FUJIAN AREA AND ITS TECTONIC IMPLICATIONS LI Qiang, WU Jian-ping SEISMOLOGY AND GEOLOGY    2023, 45 (4): 970-986.   DOI: 10.3969/j.issn.0253-4967.2023.04.010 Abstract （418）   HTML （29）    PDF（pc） （6249KB）（356）       Knowledge map    Save The Fujian area is located tectonically at the southeastern margin of the South China continent, which consists of three sub-blocks, the northwest Fujian block, the southwest Fujian block and the east Fujian block. This region is the forefront of the interaction between the Eurasian plate and the Philippine Sea plate. Geologically, the Fujian area has undergone a complex tectonic evolution process, and the huge intrusive-volcanic rocks formed by multi-stage tectonic changes were widely exposed in this region. Since the inversion of the crustal three-dimensional P-wave velocity structure was important for understanding the tectonic evolution process and the deep seismogenic environment in the region, a lot of research work has been carried out in Fujian area, including seismic body wave tomography, ambient noise surface wave tomography and artificial seismic profiles. Although some important features of the crustal velocity structure in this region had been obtained by natural seismic body wave or ambient noise surface wave imaging, the grid lateral resolution was relatively poor(generally above 0.5° horizontally), which made it difficult to constrain effectively the detailed features of the fault zone velocity structure in this region. For example, the Fu'an-Nanjingfault zone, as an important fault zone in the region, which controlled the magmatic intrusion activities before the Mesozoic, the features of its deep velocity structure have been rarely revealed. Although the resolution of artificial seismic profiles was high, it covered a relatively limited detection range in this region. In this paper, 3203 natural local earthquakes were selected using the observation reports of Fujian seismic network from 1999 to 2021 and integrating some data from neighboring provinces, which includes both 76423 absolute arrival time data and 389021 P-wave relative arrival time data from131 seismic stations. The test results of checkboard showed that the northwest Fujian block had poor recovery at all depths due to the limited internal seismic ray coverage, most areas of the southwest Fujian block had good recovery at all depths, and the east Fujian block could been recovered at all depths except for its northern region which had poor recovery at 0km, 25km and 30km depth. Under this resolution condition, the three-dimensional crustal P-wave fine velocity structure in Fujian region was obtained. The arrival time residual conforms to a Gaussian distribution before and after the inversion. The travel time residuals of the seismic phases were mainly distributed in the range of -1.5 to 1.5s before the inversion, and these travel time residuals of the seismic phases were mainly distributed in the range of -0.5 to 0.5s after this inversion. The travel time residuals were reduced significantly and were more concentrated around 0. Using the velocity structure obtained from the inversion and combining with the geological structure and geophysical field characteristics of this region, the tectonic implications which may be related to these features of velocity structure in the region were discussed. The main results are as follows: (1)In the near-surface shallow layer, the P-wave low-velocity feature is mainly correlated better with the NW-trending faults, such as the Nanri island fault, Meizhou bay fault, Yong'an-Jinjiang fault and Jiulong river fault. This may be related to the relatively young activity age and more fragmented shallow parts of the NW-trending faults. The lateral variation of velocity is small in the middle and upper crust at 5km and 10km depths relative to other depths, but there is a relatively high velocity zone of P velocity in northeastern Fujian area. (2)The P-wave velocity structure shows generally a relatively low velocity feature at 15~25km depth within the southwest Fujian block, especially in the south of the Yong'an-Jinjiang fault zone. Although the range distribution of this low velocity anomaly is relatively large, the magnitude of the anomaly is not large, and the upper crust and the bottom of the lower crust in the southwest Fujian block do not show this anomalous feature. On the other hand, the magnetotelluric sounding of the middle and lower crust of this block shows a high resistivity and the receiver function shows a low Poisson's ratio, this suggests that the low-velocity feature of this block is not caused by partial melt or ductile shear zone, but may be mainly caused by the more quartz-rich composition of the regional crust. (3)There exist two P-wave low velocity anomalies in the middle-lower crust of the East Fujian block, which are below the two high thermal anomalous area of the geothermal heat flow in this region. It may suggest that the formation of these two relative low velocity anomalies may be related to the transformation of the coastal area into an extensional environment and the upwelling of deep mantle materials caused by the high-angle retraction of the Paleo-Pacific plate in the late Yanshanian period. (4)The P-wave velocity features show that the velocity at the two sides of the Fuan-Nanjing fault zone is different obviously in the middle and lower crustal depths. This may imply the Fu'an-Nanjing fault has a certain control on the distribution of crustal velocity structure in the region, which is consistent with its deep characteristics of cutting the Moho interface which reflected by the Bourg gravity anomaly and aeromagnetic anomaly, which further confirms that it is a major deep fault zone in the region. Table and Figures | Reference | Related Articles | Metrics

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RESEARCH PROGRESS AND PROSPECT OF SEISMIC FLUID GEOCHEMISTRY IN SHORT-IMMINENT EARTHQUAKE PREDICTION LI Ying, FANG Zhen, ZHANG Chen-lei, LI Ji-ye, BAO Zhi-cheng, ZHANG Xiang, LIU Zhao-fei, ZHOU Xiao-cheng, CHEN Zhi, DU Jian-guo SEISMOLOGY AND GEOLOGY    2023, 45 (3): 593-621.   DOI: 10.3969/j.issn.0253-4967.2023.03.001 Abstract （609）   HTML （54）    PDF（pc） （2594KB）（350）       Knowledge map    Save Establishing the method of short-imminent earthquake prediction is the most effective way to reduce losses caused by earthquakes and is also an important scientific issue. In the 1960s and 1970s, research on earthquake prediction was carried out successively in China and other countries in the world, and after over 50 years of development, abundant precursor observation data and earthquake cases have been accumulated, and significant progress has been made in the research of formation mechanisms of precursor anomalies and prediction methods. Fluid is the most active component in the earth’s interior, and the fluids in various layers of the earth often carry characteristic geochemical information. The composition and variation of seismic fluid geochemistry are sensitive to changes of underground physical and chemical conditions, making them powerful indicators of seismic and tectonic activities. The formation mechanisms of fluid geochemical precursor anomalies mainly include liquid mixing, water-rock reaction, deep magma upwelling, seismic wave vibration, pore compression and pressure solubility mechanism. The fluid chemical anomalies associated with earthquakes can be attributed to the migration process of liquid mixing and the water-rock reaction mechanism caused by crustal stress changes. This paper systematically summarizes the empirical formulas on the duration of anomaly, earthquake magnitude and epicentral distance, as well as the seismic fluid geochemical models and methods for short-imminent prediction established both domestically and internationally. In addition, four types of seismic fluid geochemical techniques and methods currently used in earthquake situation consultation in China are described. Nine of the most widely used prediction methods are selected to inspect the twenty-seven cases of earthquakes containing water radon or gas radon anomalies in the Earthquake Cases of China from 1997 to 2020. Generally, these methods all show strong applicability. However, empirical formulas based on different regions of the world selected to inspect the above cases generally show weak applicability. It indicates that current earthquake prediction models or methods are only representative to a certain extent, and there are still great difficulties in practical application, which also directly affects the prediction efficiency of the fluid geochemical models applied to the judgment of earthquake three elements. Combined with our previous results, the paper puts forward the applicable theory for the precursor mechanism-based short-imminent prediction by seismic fluid geochemistry, that is, acquiring the dynamic change characteristics of the geochemical field based on the spatio-temporal dense and multi-item observation network, establishing a deep-shallow coupling anomaly genetic model based on the material cyclic reaction, and determining the temporal and spatial relationship between the evolution of regional fluid geochemical field and fluid geochemical changes at each measuring point in the fault zone. The construction of the geochemical subsystem of China Seismic Experimental Site provides a platform for capturing the short-imminent earthquake anomalies and constructing effective fluid geochemical anomaly mechanisms and models. The causes and abnormal mechanism of fluid geochemistry can be revealed and the seismic fluid geochemical short-imminent prediction method can be established in the light of the principle of seeking the source by field and combining the field and source. Table and Figures | Reference | Related Articles | Metrics

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JOINT INVERSION OF THE RUPTURE PROCESS OF 2018 ML5.7 XINGWEN EARTHQUAKE BASED ON SEISMIC AND INSAR OBSERVATIONS MIAO Si-yu, ZHANG Hai-jiang, GU Ning, LI Jun-lun, TAN Yu-yang, HUA Si-bo, ZHANG Yong SEISMOLOGY AND GEOLOGY    2024, 46 (2): 397-413.   DOI: 10.3969/j.issn.0253-4967.2024.02.009 Abstract （509）   HTML （33）    PDF（pc） （5595KB）（350）       Knowledge map    Save The ML5.7 Xingwen earthquake on December 16, 2018 is very likely induced by shale gas hydraulic fracturing, which caused not only massive landslides and rock collapse, but also some casualties in the surrounding area, with the direct economic loss of about 50 million CNY. It is of great significance to determine the source rupturing process of such an induced earthquake with large magnitude. Finite fault inversion is one of the commonly adopted methods to determine coseismic slip displacement distribution. For finite fault inversion, various data have different sensitivities to various aspects of the rupture process. The seismic data can provide the historical information about the earthquake rupture process because it contains the Doppler effect of the space-time rupture behavior on the fault. In comparison, the near-field geodetic data(such as InSAR and GPS)can constrain the fault parameters and the static slip distribution well because they contain the surface motion information. Therefore, the reliability of the inversion for the complex seismic rupture process can greatly be improved by combined use of seismicdata and InSAR data. In this study, strong-motion seismic data recorded at 8 near-field stations are chosen and filtered by a band-pass of 0.15-0.60Hz. The same InSAR data used in Wang et al.(2022)is adopted in this joint study. For inversion, a sufficiently large potential fault plane of 15km long and 10km wide is chosen and divided into 15×10 subfaults. Finally, the rupture process is obtained by joint inversion of strong-motion seismic data and InSAR data. The results show that the earthquake is characterzied by a typical unilateral rupture with the rupturing direction nearly towards the north. The duration of the rupture process was 6s, and the energy release was mainly concentrated in the first 5s. The rupture process is segmented and can be divided into two stages. The first stage is distributed from 1-3s and is located in the range of 0~5km from the source; and the 2nd stage is distributed from 3-5s and is located between 6 and 8km from the source. The coseismic slip is mainly concentrated in areas shallower than 5km, with a peak slip of approximately 0.27m. This can be used to explain why the Xingwen earthquake with a magnitude of ML5.7 caused relatively serious damages. Combined with the distribution of foreshocks and aftershocks, it can be seen that the foreshocks were mainly concentrated to the eastern edge of the major coseismicslip zone, which are close to some hydraulic fracturing wells. This suggests that these foreshocks occuring at the edge of the main rupture zone has a certain correlation with fluids, and the presence of fluids further leads to the fault weakening of the mainshock due to the increase of pore pressure and the decrease of effective compressive stress, which plays a triggering role in the occurrence of the Xingwen earthquake. The aftershocks are mainly distributed around the main slip zone, which are caused by after slips after the mainshock. The results from seismic inversion, InSAR inversion and joint inversion of the two data types reveal that the Xingwen earthquake is a northward unilateral rupture. The rupture propagation direction and coseismic slip distribution may be related to the physical property changes along the fault plane. Compared with the two single inversion results, the joint inversion overcomes the influence of uneven distribution of seismic stations, improves the resolution of slip distribution, and produces results that are more consistent with the real physical process. The slip model obtained by joint inversion in this study can be helpful for further understanding the mechanisms of induced earthquake, the correlation between induced earthquake and geological structure, earthquake disaster assessment and post-earthquake disaster prevention and hazard mitigation. Table and Figures | Reference | Related Articles | Metrics

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A CENTENNIAL PUZZLE OF THE EVOLUTION OF THE YANGTZE RIVER: RETROSPECTION AND PROGRESSES GUO Ru-jun, WEI Chuan-yi, LI Chang-an, ZHANG Yu-fen, LI Ya-wei, SUN Xi-lin, ZHANG Zeng-jie, LENG Yong-hui, SU Jian-chao, LI Guo-nai, LÜ Ling-yun, CHEN Xu, DING Zhi-qiang SEISMOLOGY AND GEOLOGY    2023, 45 (1): 1-28.   DOI: 10.3969/j.issn.0253-4967.2023.01.001 Abstract （770）   HTML （72）    PDF（pc） （9173KB）（349）       Knowledge map    Save The evolution history of the great rivers is one of the most important subjects in earth science, especially, the capture events and changes of great rivers which originate from the inner area of the Qinghai-Tibetan plateau and flow into the ocean are hot problems for geomorphology and geology. The Yangtze River is a representative river link with the Qinghai-Tibetan plateau and the Pacific Ocean, formation of the Yangtze River is considered an important mark ofthe Chinese landscape formation and the establishment of the modern geomorphic pattern of the East Asia. The evolution of the Yangtze River is closely linked to the uplift of the Qinghai-Tibetan plateau and the birth of the margin seas and monsoon evolution. In this study, we concluded the main debates on the evolution of the Yangtze River for more than one century, and the progresses of provenance analysis applied to the continental and sea basins of the Yangtze River in the past two decades. We collected the provenance analysis results from typical sedimentary depositions in the Yangtze River catchment, including the Xigeda Formation in the Panzhihua-Xichang area of the upper reaches, Cenozoic sedimentary of the Jianchuan Basin which is near the First Bend of Shigu, Gravel Layers in the middle and lower reaches, borehole sediment of the Jianghan Basin and Yangtze River Delta, and sediment of the marginal sea basins(Yinggehai Basin, Taiwan Island). We conclude that: 1)the debates on the evolution of the Yangtze River are still focused on two questions: when the Three Gorges was formed and whether south flowed off the palaeo-Jinsha River in the First Bend of the Shigu, but the debates have extended to the palaeo-drainage model in East Asia during the Cenozoic period, geomorphic formation history and exhumation-deposition process of the SE Tibet, high elevation-low relief surface formation in the SE margin of the Tibet and many important issues. 2)There is no consensus regarding the formation time and process of the Three Gorges and the First Bend, the formation time, process, and mechanism of the Yangtze River are still vigorously debated. There are mainly two views on the Miocene and early-middle Pleistocene for the formation time of the Yangtze River and mainly three paleo models of the upper Yangtze, south flow, east flow, and southeast flow. The provenance of gravel layers in the middle and lower reaches of the Yangtze River and boreholes sediment in the Jianghan Basin have complex source regions. Because of the extreme stability and multiple recycle of the detrital zircons, it is difficult to distinguish the provenance signals of the upper reaches of the Yangtze River effectively from the modern and Cenozoic sediment in basins based on the detrital zircon U-Pb age, whether the “Yangtze Gravel at Nanjin” represents the age of the Yangtze River is still strongly debated. There is still no agreement on the initial signal of the sediment of the upper Yangtze River from the boreholes record in the Jianghan Basin and the Yangtze River Delta. The boreholes deposition age is also controversial. The provenance implications of the Cenozoic sediment of the Jianchuan Basin and the Xigeda Formation for the south flow(east flow)of the Jinsha River are widely debated. The marginal sea sediment provenance signals that constrain the evolution model between the Yangtze and the Red River are also controversial. 3)There is a big difference between the drainage catchment of the paleo-Yangtze and modern Yangtze, in the provenance analysis of the sedimentary basins of the Yangtze River, suggesting constrain provenance area by multi-mineral and multi-index and strengthen the comparison between the continental and marginal sea basins. The evolution history of the Yangtze River will be reconstructed more comprehensively from the perspective of geomorphology, tectonic evolution, sedimentary paleogeography and climate change. Table and Figures | Reference | Related Articles | Metrics

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THE ANALYSIS OF THE STARTING YEAR AND THE COM-PLETENESS OF SEISMIC RECORDS FOR EARTHQUAKES WITH MAGNITUDES M≥7 IN THE BORDER REGION OF SICHUAN, YUNNAN AND TIBET ZHOU Jie-yuan, ZHOU Qing, RAN Hong-liu SEISMOLOGY AND GEOLOGY    2023, 45 (4): 914-935.   DOI: 10.3969/j.issn.0253-4967.2023.04.007 Abstract （401）   HTML （17）    PDF（pc） （8795KB）（346）       Knowledge map    Save Earthquake catalog is the foundational data for analyzing seismic activity, assessing seismic hazard, and studying earthquake prediction. The majority of historical earthquake records are sourced from historical documents, with a significant portion of these records found in local gazetteers. Compiling historical literature is an essential way in analyzing seismic activity because historical accounts of earthquakes often provide more detailed and accurate information than geological data. Among these sources, analyzing relevant content in local gazetteers, such as the historical development of local governance, military garrison, official records, and descriptions of disasters and auspicious events, plays a crucial role in seismic activity research. This article aims to acquire historical earthquake records by consulting local gazetteers, folk books, and other historical sources containing natural, social, and political records. These records serve as historical foundations for analyzing the completeness of seismic data records. The border region between Sichuan, Yunnan, and Tibet is located in the northwest secondary block of the Sichuan-Yunnan block, which is one of the areas with frequent strong earthquakes in China. The Xianshuihe fault zone and the Jinshajiang fault zone are the northeastern and northwestern boundary faults of the Sichuan-Yunnan block, respectively. They are large-scale and highly active fault zones formed due to the eastward escape of the Tibetan plateau caused by the relative movement between the Indian and Eurasian plates. Previous studies on active tectonics have shown that major earthquakes with magnitudes of 8 and above, as well as over 80% of strong earthquakes with magnitudes of 7, mainly occur in the boundary zones of active blocks with intense structural deformation and high stress accumulation. Moreover, the known active faults in the study area, such as the Batang fault and Litang fault, are also major faults that significantly have influence on the occurrence strong earthquakes. The Sichuan-Yunnan-Tibet adjacent region is home to significant infrastructure, including the Sichuan-Tibet railway and hydropower stations. Analyzing the completeness of earthquake data in the border region of Sichuan, Yunnan, and Tibet can contribute to the assessment of fault hazards and the analysis of regional seismic activity trends. This, in turn, can help minimize the damage caused by earthquakes to critical infrastructure and further enhance the safety and security of people’s lives and properties. This study reviewed the local gazetteers of 44 counties in the border region between Sichuan, Yunnan, and Tibet, and summarized the establishment and historical evolution of each county. Based on the analysis of the road evolution from Sichuan to Tibet and from Yunnan to Tibet, we examined the significant roles of important transportation hubs and nodes, such as stations, pond flood, and grain platforms, in regarding of recording earthquakes. Combining various historical sources and previous research on the completeness of earthquake data in the region, we conducted a comprehensive analysis to determine the probable starting years for the availability of seismic records of magnitude 7 and above in the Xianshuihe area and the three parallel rivers area. Additionally, based on the data of the length and short axis of isoseismal lines from 88 earthquakes, an elliptical model was used to derive the seismic intensity attenuation relationship for the Sichuan-Yunnan block. By placing the fitted isoseismal lines of magnitude 6 and 7 earthquakes in the study area, we analyzed their impact range, providing a spatial dimension basis for the completeness analysis of seismic data. This article provides a comprehensive analysis and demonstration of the complete starting years of seismic data in the border region between Sichuan, Yunnan, and Tibet from both temporal and spatial perspectives. The results indicate that due to the establishment of grain stations and Tangxun along the Sichuan-Tibet road, as well as the appointment of officials, several counties in the Xianshuihe area, including Kangding, Luhuo, Garzê, Litang, and Yajiang, were developed between 1719 and 1736. At the same time, there are relatively abundant historical documents related to earthquakes in the Xianshuihe area. Local chronicles, reports from governors and resident ministers, written records in Tibetan temples, and accounts from lamas have documented earthquake surveys, disaster assessments, and relief efforts. By combining these historical sources with the analysis of intensity attenuation relationships in the Sichuan-Yunnan block, the affected areas of earthquakes with magnitudes 6 and 7 can be determined that the period from 1719 to 1736 marks the starting years with complete M≥7 earthquake data in the Xianshuihe area. The towns of Batang, Mangkang, and Changdu in the three parallel rivers area are also significant nodes and hubs along the road to Tibet. They were established with administrative institutions and granaries between 1719 and 1728, and the road network extensively covered Tangxun in the region. In considering the seismic records and historical sources in the three parallel rivers area, as well as referencing the recording capabilities of granaries, administrative institutions, and Tangxun in the Xianshuihe area, and estimating the potential recorded seismic magnitudes based on the intensity attenuation relationships of the Sichuan-Yunnan block, it can be suggested that the period from 1719 to 1728 is a possible starting point for complete earthquake data with M≥7 in the three parallel rivers area. In areas farther away from the road to Tibet, such as Jiangda, Gongjue, Baiyu, Xinlong, and the northern regions of Batang and Litang, as well as the large contiguous regions of Derong, Xiangcheng, Daocheng, and Jiulong, the eastern boundary is the Xianshuihe fault zone, while the area between the two zones is divided by the northeast-oriented Batang fault. Previous seismic geological investigations have found that within the aforementioned regions, the influence of the Jinshajiang fault zone extends along the Batang-Derong-Benzilan line. In remote areas away from the road and with sparse population, the possibility of individual earthquakes with magnitudes above 7 occurring but being missed cannot be ruled out. However, in other areas not located on active fault zones, it can be considered unlikely to experience earthquakes with magnitudes above 7. Based on the analysis of the data, the starting years of earthquakes with a magnitude of 6 and above should be the same as those of earthquakes with a magnitude of 7 and above. However, according to the analysis of the average occurrence rate of earthquakes per year, there is a significant lack of records for earthquakes of magnitude 6 and above. This may be due to the sparsely populated and vast nature of the Tibetan region during historical times, limited administrative capabilities of officials, and lack of earthquake historical records and documents. Therefore, it is not possible to determine the exact starting year for complete data on earthquakes of magnitude 6, which would be the same as for earthquakes of magnitude 7 and above. Table and Figures | Reference | Related Articles | Metrics

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PRECISE RELOCATION OF SMALL-TO-MODERATE-SIZED EARTHQUAKES IN THE DATONG VOLCANIC GROUP AND SURROUNDING AREAS XU Yong-qiang, LEI Jian-she SEISMOLOGY AND GEOLOGY    2024, 46 (2): 336-356.   DOI: 10.3969/j.issn.0253-4967.2024.02.006 Abstract （758）   HTML （42）    PDF（pc） （14298KB）（341）       Knowledge map    Save In the present study we collect a large amount of arrival times from 3 218 earthquakes in the Datong volcanic group and surrounding areas from January 2008 to January 2023 through the China Seismic Network Center and relocated these earthquakes using double-difference location algorithm, finally obtain 2 447 relocate earthquakes. Our result shows that most earthquakes occurred above a depth of 16km, and earthquakes in the basin occurred at depths of 5-16km. There are fewer earthquakes occur near the surface at depths of 0-2km, while 6km and 11km are the dominant depths for earthquakes. The overall strike trending of these earthquake sequences is NE-SW, which is consistent with the regional active faults and controlled grabens and semi-graben-type faulting basins. In addition, these earthquakes are more concentrated near the Kouquan fault zone and in the Datong-Yanggao earthquake zone in the eastern part of the volcanic group. The average location errors of these earthquakes in the east-west, north-south, and vertical directions are about 0.21km, 0.22km, and 0.30km, respectively, with an average travel time residual of 0.14s. The earthquakes near the Kouquan fault zone changed from deeper and more concentrated in the south to shallower and more scattered in the north. The earthquake sequences in the northern part of the southern section and the southern part of the middle section of the Kouquan fault zone are deeper along the NE-SW direction, roughly vertically distributed on the Kouquan fault. The earthquake sequences in the northern part of the middle section of the Kouquan fault zone did not occur on the Kouquan fault, and the distribution of earthquakes is relatively scattered, and earthquakes with larger magnitude are mostly concentrated at shallow depth, which may be related to the thick sedimentary coal-bearing strata and mining activities in the area. The strike trending of these earthquakes in the northern section of the Kouquan fault zone is, along the NE-SW direction, roughly distributed on the Kouquan fault. However, there are also earthquakes in the northern part of the Kouquan fault zone, which may suggest that the activity of the Kouquan fault zone has extended there. The focal depth in the source areas of the Datong-Yanggao earthquake is mostly concentrated at depths of 3-16km on the hidden fault parallel to the NE-SW trending Dawangcun fault to the east. The hidden fault has a large dip angle and dips towards NW, which intersects with the Tubao fault and the Liulengshan piedmont fault, likely related to the aftershock activity of the Datong-Yanggao earthquake. Earthquakes occur frequently in the middle section of the Huairen fault, followed by the southern section, and there are few earthquakes in the northern section. The seismic activity of the Shuiyu fault, the east fault of the Cailiangshan mountains, and the Yanggao-Tianzhen fault is relatively weaker. There are some seismic activities in the central part of the northern margin fault of the Tianzhen-Yanggao Basin. Earthquakes in volcanic areas occurred at the boundaries of volcanic clusters, while the seismicities inside the volcanic group area were not very strong, which suggests that the boundary of volcanic clusters is more prone to stress accumulation and earthquake generation than the interior of volcanic clusters. Based on the new seismic results of ambient noise tomography in the area, it is found that earthquakes are not only related to faults, but more importantly, most earthquakes occur near the high-to-low-velocity anomaly boundaries. Furthermore, there are obvious low-velocity anomalies visible beneath most earthquake source areas, which may suggest that the occurrence of these earthquakes is closely related to fluids carried by the upwelling of thermal materials rising to the crust from the mantle and reducing the effective normal stress on the fault planes. Table and Figures | Reference | Related Articles | Metrics

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INVESTIGATION OF THE SEISMOGENIC STRUCTURE OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG BASED ON THE TECTONIC STRESS FIELD PERSPECTIVE SHENG Shu-zhong, WANG Qian-ru, LI Zhen-yue, LI Hong-xing, ZHANG Xiao-juan, GE Kun-peng, GONG Meng SEISMOLOGY AND GEOLOGY    2025, 47 (1): 49-63.   DOI: 10.3969/j.issn.0253-4967.2025.01.004 Abstract （929）   HTML （28）    PDF（pc） （3649KB）（332）       Knowledge map    Save On January 7, 2025, at 09:05 Beijing Time, an MS6.8 earthquake struck Dingri County in Shigatse City, Xizang, as reported by the China Earthquake Networks Center. The earthquake occurred at 28.50°N, 87.45°E with a hypocentral depth of 10km, resulting in significant casualties and economic losses. In the immediate aftermath, major earthquake research institutions and seismologists, both domestic and international, promptly released the focal mechanism solution, providing crucial data for understanding the earthquake's origin and its seismogenic structure. However, the two nodal planes of the focal mechanism, derived from a double-couple source model, are equivalent, necessitating additional data or methodologies to distinguish the actual seismogenic fault plane. The parameters of the seismogenic fault are fundamental for the accurate calculation of ground motion maps, and they provide key information for seismic hazard assessment and post-earthquake rapid response guidance. Therefore, it is imperative to identify the seismogenic fault plane for the given focal mechanism solution. This study employs the tectonic stress field in the source region of the Dingri earthquake to calculate the instability coefficients of the two nodal planes, selecting the most unstable plane as the actual seismogenic fault. This method is based on the tectonic stress field to identify the seismogenic fault plane in the two nodal planes of the focal mechanism solution. The approach is applied to identify the seismogenic fault plane of the Dingri earthquake and nearby historical seismic events. Using the Global Centroid Moment Tensor(GCMT)focal mechanism solution, the study inverts the shallow tectonic stress field in the source region. The results reveal the maximum principal compressive stress axis is nearly vertical, and the maximum principal tensile stress axis is nearly horizontal with a strike orientation of E-W, which is a normal faulting stress regime. The stress field result is consistent with the normal faulting characteristics of the regions main fault structures. The seismogenic fault for the Dingri 6.8 earthquake is the one-striking southward and dipping westward nodal plane of the focal mechanism solution, determined to be a normal fault. Thus, we can infer that the seismogenic fault is the Dengmocuo Fault. In addition, the identification of the seismogenic fault for the historical earthquakes in the Dingri area shows that the fault is characterized by a southward strike and westward dip, with dip angles ranging from 37° to 48°, and the fault type is normal faulting. Identifying the seismogenic fault plane in the nodal planes of the focal mechanism solution based on the tectonic stress field, this study accurately identifies the seismogenic faults associated with the Dingri earthquake and surrounding historical events. It contributes seismological evidence for understanding the seismogenic structure of the region. It offers valuable insights for future research on seismogenic structures, particularly the determination of seismogenic faults of small and medium-magnitude earthquakes. Table and Figures | Reference | Related Articles | Metrics

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ANALYSIS OF BUILDING DAMAGE AND CASUALTIES OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG BASED ON FIELD INVESTIGATION WEI Ben-yong, ZHANG Yu-man, SHI Feng, QIAO Jun-xiang, WANG Xin, ZHANG Da SEISMOLOGY AND GEOLOGY    2025, 47 (1): 64-79.   DOI: 10.3969/j.issn.0253-4967.2025.01.005 Abstract （720）   HTML （20）    PDF（pc） （10539KB）（324）       Knowledge map    Save On January 7, 2025, at 9:05 AM, a magnitude 6.8 earthquake struck Dingri County, Shigatse City, located in the southern part of the Xizang Autonomous Region(28.50°N, 87.45°E), with a focal depth of 10 kilometers. By 7:00 PM on January 9, the earthquake had resulted in 126 fatalities and 188 injuries. A total of 27, 248 buildings were damaged, including 3, 612 collapsed structures. Timely understanding and analysis of the earthquake's damage characteristics and the causes of casualties can provide valuable references for subsequent disaster loss assessments and recovery planning. Based on field investigations, this study provides a comprehensive overview of the earthquake damage, covering four main aspects: seismic characteristics and affected areas, seismogenic fault and aftershock distribution, building damage and influencing factors, and the distribution and causes of casualties. The study also analyzes in detail the reasons for the severe casualties in this earthquake. The epicenter of the Dingri earthquake is located within the Lhasa block of the Tibetan Plateau. The earthquake was triggered by the Dengmecuo fault, a normal fault characterized by crustal extension due to fault slip. The maximum intensity of this earthquake reached IX degree, and the major axis of the isoseismal line runs nearly north-south, with a length of 191 kilometers and a short axis of 152 kilometers. The area affected by intensity VI or higher is approximately 23986 square kilometers, covering six counties and 45 towns(or streets)in Shigatse City, Xizang Autonomous Region. The earthquake caused a surface rupture of approximately 26 kilometers, with a maximum vertical displacement of about 3 meters. Field investigations revealed that the building structures in Dingri County mainly consist of frame, masonry, and traditional civil structures. Among these, traditional civil structures sustained the most severe damage. In extremely and severely affected areas, the majority of civil-structure buildings were either destroyed or severely damaged, with complete or partial collapses occurring. The main factors contributing to the severe damage to civil-structure buildings include the lack of seismic resistance measures, poor construction techniques, and inadequate shear resistance and bond strength of construction materials. The majority of casualties were concentrated in Changsuo, Cuoguo, and Quluo towns, near the epicenter. Changsuo town suffered the most severe damage, with casualties accounting for 74.60% of the total fatalities. The high casualty rate can be attributed to the strong destructive power of the earthquake, the proximity of villages to the fault lines, low seismic performance of buildings, high population density, and adverse environmental conditions such as low temperatures and oxygen deficiency. Based on the analysis of the causes of casualties and field investigations, this study proposes targeted countermeasures and suggestions to mitigate earthquake disaster risks and minimize casualties in Xizang. These measures include enhancing active fault detection, improving earthquake early warning capabilities, reducing seismic damage risks to traditional residential buildings, strengthening emergency response measures, mitigating the risk of secondary earthquake disasters, and increasing public awareness of earthquake risks. These recommendations aim to enhance the region's earthquake prevention and mitigation capabilities and provide guidance for post-disaster recovery and reconstruction. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE RELATIONSHIP BETWEEN LITHOSPHERIC MAGNETIC FIELD AND GEOLOGICAL STRUCTURE AND SEISMIC ACTIVITY: TAKING THE 2021 MS6.4 YANGBI EARTHQUAKE AS AN EXAMPLE CHEN Zheng-yu, NI Zhe, ZHOU Si-yuan, JIN Yun-hua, YANG Xin-jun SEISMOLOGY AND GEOLOGY    2024, 46 (2): 449-461.   DOI: 10.3969/j.issn.0253-4967.2024.02.012 Abstract （510）   HTML （17）    PDF（pc） （5142KB）（322）       Knowledge map    Save The lithospheric magnetic field is an important part of the earth’s magnetic field, which is affected by many factors, such as rock’s magnetization environment, underground geological structure, rock mineralogical composition, thermal and pressure state, and the deep tectonic evolution process. Most earthquakes occur in the crust and uppermost mantle, known as the lithosphere. The preparation and occurrence of earthquakes are usually accompanied by long-term accumulation and sudden release of energy, which will lead to changes in the thermal and pressure state of rocks, causing magnetic susceptibility variation in the lithosphere. Previous studies show that seismic activities can cause abnormal changes in the geomagnetic field, and there is an obvious correlation between the lithospheric magnetic field and seismic activities. The MS6.4 Yangbi earthquake on May 21, 2021, provided a unique opportunity to study the dynamic evolution of seismo-magnetic anomaly. Five-term repeat station vector geomagnetic data observed in Yangbi and surrounding areas from 2018-2021 were used in this paper, the first four terms were observed before the earthquake, and the fifth term was observed after the earthquake. After data processing and model calculation, the lithospheric magnetic fields before and after the earthquake are obtained, lithospheric magnetic field models are established using the Surface Spline method, and annual variations are calculated. Based on the analysis of lithospheric magnetic field combined with the regional geological structure, the Northwest Sichuan Subblock shows negative magnetic anomalies, which is consistent with the geological structural characteristics in the study area, altitude and crustal thickness increase sharply from Central Yunnan Subblock to Western Sichuan Plateau. Small areas of positive and negative magnetic anomalies are alternatively distributed in the Central Yunnan Subblock, which reflects the heterogeneity of deep lithosphere structure. The negative magnetic anomaly in the western boundary of the study area is also consistent with the geological characteristics of the Qingzang Plateau. There is also a correspondence between lithospheric magnetic field anomalies and faults, especially the total intensity. Negative magnetic anomaly strips are distributed along the strike of the Honghe Fault and Lijiang-Xiaojinhe Fault, while Weixi-Qiaohou-Weishan Fault appears at the junction of positive and negative magnetic anomalies. The statistical analysis of the MS6.0 and above seismic events from 1970 to 2021 shows that there is a correlation between lithospheric magnetic anomalies and seismic activities. Most earthquakes occur in the weak magnetic anomaly area, especially near zero contour. The earthquakes tend to be distributed in anomaly gradient belts, and the number of earthquakes in the negative anomaly area is higher than that in the positive anomaly area. Analyzing the characteristics of the pre- and post-seismic changes of declination and total intensity near the epicenter of Yangbi MS6.4, it is found that the epicenter of the Yangbi earthquake is located near the zero-contour-line of declination. During the preparation of the Yangbi earthquake, the total intensity gradually changed from a balanced distribution of positive and negative anomalies to the overall negative changes, and the magnetic anomalies recovered the trend of the balanced distribution of positive and negative changes after the earthquake. Table and Figures | Reference | Related Articles | Metrics

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THE LATE QUATERNARY ACTIVITY CHARACTERISTICS AND SLIP RATE OF BATANG FAULT IN SE TIBETAN PLATEAU HUANG Wei-liang, ZHANG Jia-le, XIANG Wen, YANG Qian-hao SEISMOLOGY AND GEOLOGY    2023, 45 (6): 1265-1285.   DOI: 10.3969/j.issn.0253-4967.2023.06.002 Abstract （407）   HTML （37）    PDF（pc） （17828KB）（321）       Knowledge map    Save The southeastern margin of the Tibetan plateau is one of the most intensely deformed regions in the continental crust. A series of active faults with varying lengths and mechanical properties have segmented the lithosphere into multiple active blocks, with the Sichuan-Yunnan block being one of the most tectonically active regions. Its eastern boundary is characterized by secondary fault zones such as the Xianshuihe-Anninghe-Zemuhe, Xiaojiang, and Daliangshan fault zone, forming a narrow and continuous strike-slip deformation zone with a total length exceeding 1 100km. The western boundary of the Sichuan-Yunnan Block is mainly composed of the Jinsha River and the Red River fault zone, with the Jinsha River fault zone consisting of more than 20 roughly parallel secondary faults, forming a complex fault zone with 30~200km width. Despite recent GNSS network observation revealing the current tectonic deformation rates in this region, there is still a lack of research on the deformation characteristics and rates of individual active faults. This limitation makes it difficult in the assessment and understanding of seismic hazards in the area, restricting the scientific understanding of the current deformation mode in the southeastern margin of the Tibetan plateau. The Batang Fault, located within the Jinsha River fault zone at the western boundary of the Sichuan-Yunnan block, is a NE-trending main fault that obliquely cuts across the Jinsha River Fault, dividing later into northern and central segments. Presently, the Batang Fault is characterized by dominant right-lateral strike-slip motion. The deformation characteristics and rates of this fault since the Late Quaternary are crucial for understanding the spatial distribution of strong earthquakes and deformation patterns in the Sichuan-Yunnan block. The Batang Fault has a total length of 115km and is a Holocene right-lateral strike-slip active fault. The fault extends along the margins of bedrock mountains on both sides of the Maqu river and Jinsha River valleys, trending NNE or NWW to SEE, with a steep dip. The fault exhibits linear distribution of topographic features such as slopes, ridges, triangular facets, and fault scarps, essentially controlling the boundaries of bedrock mountains. In view from the geomorphology, the Batang Fault appears continuous and straight without distinct segmentation, except for localized small-scale step-like features. The Batang Fault has preserved abundant Late Quaternary activity evidence in two areas, Huangcaoping village and Batang county. This study utilized unmanned aerial vehicle photogrammetry to establish sub-meter digital terrain data for Huangcaoping and Batang site, accurately measuring displaced features such as alluvial fans and gullies affected by faulting. In Huangcaoping site, the fault has cut through multiple mountain-front alluvial fans, causing varying degrees of horizontal displacement in features such as gullies and the margin of the alluvial fans. This provided a scale for quantifying fault displacement. In Huangcaoping, five large-angle gullies intersect with the fault, one of which is a large gully developed in the bedrock mountain area. The gully has a deep incision, a narrow valley, and a rapid downstream turn to the right after exiting the mountain. The left bank of the gully preserves two geomorphic surfaces, Qo(older)and Qi(younger)surface, with the fault cutting across both surfaces, forming linear steep terrain. The measured total right-lateral offset of this gully since exiting the bedrock mountain area is(46±9)m. To constrain the activity rate of the Batang Fault at this location, we used cosmogenic nuclide single clast dating to determine the exposure age of the oldest geomorphic surface, Qo, as(12.5±0.5)ka. Considering that the formation of the river predates the Qo geomorphic surface, the age-constrained slip rate of the fault at this location is considered a maximum value, estimated at(3.6±0.8)mm/a. At Batang county, the Batang Fault has preserved clear faulted topography when cutting through the Moqu alluvial fan. The southern edge of the Moqu alluvial fan has been displaced by the fault, providing a well-preserved geomorphic marker for determining the strike-slip displacement of the fault. The Batang Fault, when intersecting the steep edge of the Moqu River alluvial fan, caused an obvious right-lateral offset, determined by comparing the consistent morphology of the steep edge on both sides of the fault. The right-lateral strike-slip displacement along the southern edge of the alluvial fan is measured at (40±5)m. The cosmogenic nuclide depth profile dating was used to determine the age of the faulted alluvial fan. From a vertical profile excavated along a man-made road on the edge of the alluvial fan, four mixed samples of small pebbles were collected from bottom to top. The calculated exposure ages of the debris flow alluvial fan are (15.2+3.2/-5.4)ka (without consideration of erosion)and (16.4+3.9/-5.6)ka (with consideration of erosion). Combining the fault displacement along the southern edge of the alluvial fan and the cosmogenic nuclide depth profile ages, the slip rate of the Batang Fault at this location is estimated to be of(2.6±0.6)mm/a (without erosion)or(2.4±0.8)mm/a (considering erosion). We believe that the age results with consideration of erosion effects is closer to the true values, thus we take 2.4mm/a as the activity rate of the Batang Fault at this location. The two slip rate values of the Batang Fault obtained in the Huangcaoping and Batang county sites are similar, indicating a right-lateral strike-slip rate of 2~4mm/a since the Late Quaternary. This rate accounts for 50%~80% of the present GPS observation shear deformation across the western boundary of the Sichuan-Yunnan block, indicating that the Batang Fault is a major deformation absorption zone in the Jinsha River fault zone. However, this rate is lower than the predicted~10mm/a using block models. The discrepancy may be due to the different understanding of the deformation mode at the western boundary of the Sichuan-Yunnan Block. In the block model, block sliding mainly relies on the primary boundary fault to regulate, but the long-term and lower geological activity rate of the Batang Fault obtained in this study does not match the assumption of a higher activity rate for the boundary fault in this model. The continuous and diffuse deformation characteristics of crustal deformation in the southeastern margin of the Tibet plateau may corroborate the lower activity rate of the Batang Fault obtained in this study. Table and Figures | Reference | Related Articles | Metrics

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SEISMOGENIC FAULT OF THE TANGSHAN MS5.1 EARTHQUAKE ON JULY 12, 2020 AND ITS IMPLICATIONS FOR REGIONAL TECTONICS CAO Jun, ZHOU Yi, GAO Chen, LIU Shu-feng, CHEN An, ZHANG Su-xin, FENG Xiang-dong, WU Peng, CHEN Zhao-dong SEISMOLOGY AND GEOLOGY    2024, 46 (5): 993-1011.   DOI: 10.3969/j.issn.0253-4967.2024.05.001 Abstract （827）   HTML （64）    PDF（pc） （10827KB）（316）       Knowledge map    Save On July 12, 2020, a M5.1 earthquake occurred in the Guye District of Tangshan City. This earthquake is notable as the only moderate seismic event exceeding magnitude 5 in the Tangshan area over the past two decades. However, the exact seismogenic fault responsible for this earthquake remains undetermined, complicating efforts to assess future seismic risks in the region. Post-earthquake damage assessments revealed that the macroseismic damage was distributed along two primary fault zones: a long northwest(NW)trending band and a short northeast(NE)trending band. The most significant damage occurred at the intersection of these two bands. Based on the regional geological structure and stratigraphy, field surveys identified the NE-trending Tangshan-Guye fault as a Holocene-active fault, while the NW-trending Mozhouyu fault was classified as a Quaternary fault within the area of greatest damage. Analysis of Sentinel-1A InSAR time-series data revealed differential deformation along the Mozhouyu fault. Relocation results of earthquakes greater than magnitude 1.0 over the past decade in the Tangshan region showed seismic activity distributed in two primary bands. One band aligns with the NE-trending Tangshan-Guye fault, with concentrated activity at its intersection with the Mozhouyu fault. Following the M5.1 earthquake, multiple authorities determined that the focal mechanism indicated a strike-slip earthquake, with two conjugate planes oriented in the NE and NW directions. This finding is consistent with the alignments of the Tangshan-Guye and Mozhouyu faults. Through comprehensive analysis, including post-earthquake field surveys, regional deformation data, and the relocation of smaller seismic events, it was concluded that the surface damage from the Tangshan Guye earthquake followed both NE and NW orientations. Of the two intersecting faults in the damaged area, the Mozhouyu fault is a middle Pleistocene fault, while the Tangshan-Guye fault is the most significant Holocene-active fault in the region. The characteristics of these conjugate faults align with both the source parameters and relocated seismic sequences of the Tangshan Guye earthquake. The right-lateral strike-slip motion along the Tangshan fault zone, combined with regional NE—NEE-directed compressive stress, likely caused the Tangshan-Guye fault to be blocked by the Qinglongshan complex anticline during its eastward expansion. Subsurface data further indicate that the Qinglongshan complex anticline marks a boundary of regional physical property differences. Therefore, it is concluded that the Tangshan-Guye fault and the Mozhouyu fault were the conjugate seismogenic faults responsible for the M5.1 earthquake on July 12, 2020. The Tangshan Guye earthquake is a typical moderate-intensity strike-slip event in the North China Plain. An analysis of 705 focal mechanism solutions from 2002 to 2020 indicates that most earthquakes in the region are predominantly strike-slip in nature. Historical strong earthquakes in the North China Plain also exhibit high-angle strike-slip faults as their primary seismogenic structures, a conclusion supported by extensive seismological research. A substantial body of seismic studies suggests that the failure of the North China Craton during the early Cenozoic was driven by crustal extension, resulting in the formation of listric(shovel-shaped)normal faults. However, these faults are no longer the main seismogenic structures for present-day earthquakes. Since the late Pleistocene, tectonic activity in the North China Plain has been characterized by the development of new, steeply dipping strike-slip faults, which cut through the older listric normal faults. These steep dip strike-slip faults have become the primary seismogenic structures responsible for regional seismicity. Future seismic hazard assessments in the North China Plain should focus on the activity of these steep dip faults, as they are more likely to generate significant earthquakes. This shift in tectonic stress is attributed to a combination of factors, including the eastward expansion of the Tibetan Plateau, the rigid deformation of the Ordos Block, and the westward subduction of the Pacific and Philippine plates. Since the late Pleistocene, these forces have redefined the tectonic landscape of the region, increasing the likelihood of strike-slip faulting. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE DEEP STRUCTURAL CHARACTERISTIC OF MAIN ACTIVE FAULTS IN HENAN PROVINCE AND ITS ADJACENT AREAS XU Zhi-ping, ZHANG Yang, YANG Li-pu, XU Shun-qiang, JIANG Lei, TANG Lin, LIN Ji-yan SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1521-1538.   DOI: 10.3969/j.issn.0253-4967.2022.06.010 Abstract （864）   HTML （33）    PDF（pc） （7110KB）（306）       Knowledge map    Save There are many first-order intersecting tectonic units and different strike faults developed widely in Henan Province, and many historical earthquakes with magnitude 6 and above occurred, which have brought great losses to people’s lives and property. In order to effectively reduce the risk of earthquake disaster in Henan Province and understand the deep seismogenic environment, we have carried out a systematic study on the deep structural characteristics of these active faults. Firstly, based on the high-precision Bouguer gravity anomaly data of Henan Province and its adjacent areas, we obtained the characteristics of gravity anomaly fields at different spatial scales in the study area by using the multi-scale wavelet analysis method. Then the detailed characteristics of different orders wavelets of Bouguer gravity anomaly field in the study area and its relationship with regional structure were analyzed. We found that within 14km of the crust, the regional tectonic activity has an obvious control effect on the trend of gravity anomaly zone. The trend of gravity anomaly zones is obviously different in different tectonic units in the study area. In the north of Henan, the trend of gravity anomaly zones is NE, which is consistent with the regional tectonic trend. The horizontal density difference is obvious. In the south of North China depression and Qinling-Dabie uplift area, the trend of gravity anomaly zones is NW, NWW and EW. In the differential uplift area of western Henan, the trend of gravity anomaly zones is NE. At the 27km depth of the crust, most gravity anomalies are in a clumpy shape, and the consistency between the trend of the gravity anomaly and the regional structure decreases, indicating the differences in regional tectonic stress effect and formation process at different depths of the crust. For example, under the northward compression from Qinling-Dabie uplift, the crust structure in the south of North China depression is different, and the difference gradually decreases from shallow to deep. At the same time, with the increasing of depth, the boundary between Qinling-Dabie uplift and southern North China depression moves to the Pingdingshan and Luohe. Our results show that the regional deep faults have an obvious control over the distribution of gravity anomalies, and the linear transition zone of gravity anomalies often corresponds to the deep faults. In order to obtain the distribution characteristics of active faults in Henan Province and adjacent areas, we analyzed the wavelet multi-scale decomposition of Bouguer gravity anomaly and identified 38 faults. Based on the seismic and geological results, we interpreted the 38 faults, including10 shallow faults in the upper crust with a depth of less than 8km, 15 faults at the bottom of the upper crust with a depth of 12~14km and 13 faults in the lower crust with a depth of 27km. In the study area, the deep faults control the boundary of the first-order tectonic units, such as Liaocheng-Lankao Fault, Tangxi Fault, Xinxiang-Shangqiu Fault, etc., and many moderately strong earthquakes occurred in these faults in history. At last, we analyzed the deep tectonic environment of historical earthquakes with magnitude 6 and above in Henan Province. The results show that the historical earthquakes with magnitude 6 in Xuchang locate near the boundary zone of second-order tectonic units. Other historical earthquakes with M6.0 locate below the secondary uplift or depression controlled by deep and large faults in the crust, such as Puyang earthquake which locates in the Dongpu depression. It can be concluded that the intersections of gravity anomalies zones with different trends, the deep seated fault-controlled intra-crust low gravity anomaly areas, and the intersections of deep seated fault with different strikes are the deep tectonic background and favorable locations for generating earthquakes with magnitude 6 and above in Henan Province. The results of analysis of the characteristics of major deep active faults in Henan Province expanded our understanding of the tectonic environment of the study area and provided a geophysical basis for earthquake prevention and disaster reduction in Henan Province in the future. Table and Figures | Reference | Related Articles | Metrics

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RESEARCH ON COMPREHENSIVE STANDARDIZATION FOR SURVEYING AND PROSPECTING OF ACTIVE FAULT LI Yi-shi SEISMOLOGY AND GEOLOGY    2023, 45 (2): 455-463.   DOI: 10.3969/j.issn.0253-4967.2023.02.009 Abstract （413）   HTML （15）    PDF（pc） （926KB）（302）       Knowledge map    Save Active fault surveying and prospecting is the fundamental work for earthquake prevention and disaster reduction. China began to conduct quantitative research on active faults in the 1980s, and then carried out surveying and prospecting of active faults and seismic hazards assessment in several cities. The results provide a scientific basis for urban land planning, urban disaster prevention planning, construction project site selection and fault setbacks, potential seismic hazards investigation, earthquake emergency preparedness, etc. Standards research in surveying and prospecting of active faults began at the beginning of this century in pace with the development of professional work. Since 2013, the research on the technical system and standards system about surveying and prospecting of active faults was carried out, and a series of standards for technical methods and outcomes were compiled successively. Currently, 1 national standard and 9 sectors standards have been released, and 11 standards are in processing. The national standard GB/T 36072 “Surveying and Prospecting of Active Fault” stipulates the process, content, outcomes, and main technical methods. The 9 sectors standards cover techniques and methods consisting of remote sensing survey, fault geomorphological survey, paleo-seismic trenching, drilling, and fault strip mapping, and stipulate the requirements for the steps, technical indicators, and outcomes of the corresponding technical methods. These standards have become important technical support for active fault survey and prospecting and the main basis for operational supervision. However, there are still many gaps in the standards, and there are obvious contradictions between the supply and demand of the standards. At the same time, the compiling of standards for surveying and prospecting of active faults scattered in different periods and institutions, leading to the problems of function matching and technical indicators coordination among standards. This paper applies comprehensive standardization to surveying and prospecting of active faults, with the objectives to improve the work quality and the application benefit, by regarding the standardization object as a complete system, decomposing comprehensively the relevant elements in three aspects: business process, outcomes and application, and constructing the standard-complex of surveying and prospecting active faults. This is the first attempt to apply comprehensive standardization to the earthquake industry. The working process of surveying and prospecting of active faults can be decomposed into six steps: preparation and revision of implementation plan, determination of fault spatial distribution and parameters, identification of fault activity, analysis of the deep seismic-tectonic environment, assessment of seismic hazards of active faults, and determination of fault deformation zone width. The preparation and revision of the implementation plan comprise data collection, controlled detection, preliminary identification of fault activity, and revision of the implementation plan; the determination of fault spatial distribution and parameters include the implementation and on-site investigation of technical methods such as high-resolution remote sensing interpretation, geological and geomorphic investigation, fault geomorphological survey, geophysical exploration, drilling, paleo-seismic trenching, and dating. The relevant elements of the business process mainly include the work content, technical methods, and technical requirements for project implementation of these links, as well as the technical requirements for project implementation plan preparation and outcomes check and acceptance. The outcomes of surveying and prospecting active faults are divided into survey data, professional outcomes maps, reports, databases, etc. The relevant elements of the outcomes mainly include the technical requirements of the original data and the phased outcomes obtained from the analysis, professional outcomes maps, reports, and databases. The application of surveying and prospecting of active faults is oriented to meet the needs of disaster reduction, and its outcomes are applied to the practice of earthquake prevention and disaster reduction. Relevant elements of application mainly include technical requirements for fault classification and fault cataloging, three-dimensional modeling, hazard assessment, fault avoidance, data management, and information service system construction. Based on the analysis of relevant elements of business process, outcomes, and application, combined with the current status of existing standards, the framework structure of five sequences on surveying and prospecting of active faults standard-complex is put forward, namely, business foundation, project implementation, technical method, outcomes, and application, together with a detailed list of 41 standards. Among them there are 8 items of business foundation, 3 items of project implementation, 15 items of technology and methods, 10 items of outcomes, and 5 items of application. The standard-complex of surveying and prospecting of active faults covers the standards required by the entire business chain, and the standards are interconnected and coordinated. Taking the advantage of the complete set of standards will lay a good foundation for further improving the standardization level of surveying and prospecting of active faults and accelerating the progress of developing standards, and also provide a beneficial demonstration for the high-quality innovative and standardization development of other business areas of earthquake prevention and disaster reduction. Table and Figures | Reference | Related Articles | Metrics

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SOURCE RUPTURE MECHANISM AND STRESS CHANGES TO THE ADJACENT AREA OF JANUARY 7, 2025, MS6.8 DINGRI EARTHQUAKE, XIZANG, CHINA YANG Jian-wen, JIN Ming-pei, YE Beng, LI Zhen-ling, LI Qing SEISMOLOGY AND GEOLOGY    2025, 47 (1): 36-48.   DOI: 10.3969/j.issn.0253-4967.2025.01.003 Abstract （714）   HTML （46）    PDF（pc） （6115KB）（302）       Knowledge map    Save According to the official determination of China Seismic Network, at 09:05 on January 7, 2025, an MS6.8 earthquake(hereinafter referred to as Dingri earthquake)occurred in Dingri County(28.50°N, 87.45°E), Shigatse City, Xizang, with a focal depth of 10km. The earthquake occurred in the southern part of the Qinghai-Xizang Plateau, which is located in the intersection area of the Shenzha-Dingjie rift and the south of Xizang detachment system. The Dengmecuo fault(about 11km)is the closest to the earthquake, and the focal mechanism is tensile rupture. The earthquake had high magnitude, high intensity and shallow source, and the towns and villages in the epicenter area were relatively concentrated. In addition, the landform type of the epicenter and the surrounding area is a river alluvial plain, and the soil is soft, which amplifies the earthquake damage effect. Due to the comprehensive superposition of various factors, the earthquake caused severecasualties and building damage. The Dingri earthquake is a shallow-source normal-fault earthquake. The ground vibration and building(structure)damage caused by the release process of seismic radiation energy are higher than other earthquakes of the same magnitude, and the surface rupture characteristics are more significant. Therefore, the in-depth study of the Dingri earthquake, the acquisition of the co-seismic deformation field and the source sliding model, and the understanding of the earthquake's seismogenic mechanism and dynamic process can provide scientific and technological support for seismic damage assessment and secondary disaster analysis. In addition, based on the fault slip model, the Coulomb stress change in the surrounding area caused by co-seismic dislocation can be calculated, which is of great significance for the scientific evaluation of the future seismic risk and potential seismic disaster risk in the adjacent area. The Dingri earthquake occurred at a high altitude area, with an average elevation of about 4471m within 10km near the epicenter. The harsh natural conditions and the surrounding GNSS and strong seismic stations are scarce. Therefore, SAR images have become an important data source for obtaining the coseismic deformation of the earthquake and inversion of fault slip distribution. In this paper, based on the ascending and descending SAR image data before and after the Dingri earthquake taken by the Sentinel-1A satellite of the European Space Agency, the co-seismic deformation field of the Dingri earthquake was obtained by D-InSAR technology. On this basis, the source sliding model of the earthquake was jointly inverted based on the coseismic deformation data of the ascending and descending orbits, and the Coulomb stress variation characteristics of the surrounding area caused by the co-seismic dislocation were calculated. The deformation characteristics of the Dingri earthquake, the source rupture mechanism and the stress adjustment effect on the adjacent area are analyzed and discussed. Form the following understanding: (1)The results of the coseismic deformation field of the Dingri earthquake obtained based on the D-InSAR technology ' two-track method ' show that the long axis of the coseismic deformation field of the ascending and descending orbits is nearly NS-trending. The coseismic deformation is characterized by two obvious deformation areas in the east and west and a butterfly-like stripe pattern. The LOS deformation of the ascending and descending orbits is between -0.58~0.33m and -0.80~0.66m, respectively. (2)Based on the coseismic deformation data of ascending and descending orbits, the moment magnitude of the Dingri earthquake obtained by joint inversion is MW7.06 by using the SDM layered model method. The rupture process of the earthquake shows a unilateral rupture characteristic from the initial rupture point to the north along the fault. The fault dislocation is a standard fault mechanism with a little strike-slip component. The length of the main rupture zone of the seismogenic fault is about 55km, and the slip distribution is concentrated in the depth range of 0~15km underground. The maximum slip is 4.25m, which occurs at a depth of 8.6km underground. The main rupture zone of the earthquake has reached the surface, located about 35~53km north of the epicenter along the strike, and the potential surface rupture length is about 18km. (3)The results of the change in coseismic Coulomb stress show that the Dingri earthquake led to a decrease in coseismic Coulomb stress on both sides of the seismogenic fault. The Coulomb stress at the north and south ends of the fault rupture section and its surrounding areas increases significantly, and the loading amount is much larger than the earthquake-triggering threshold of 0.01MPa. There is a possibility of further felt aftershocks in these areas in the future. Table and Figures | Reference | Related Articles | Metrics

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FRICTIONAL PROPERTIES OF SERPENTINE MINERALS UNDER HYDROTHERMAL CONDITIONS LIU Shi-min, ZHANG Lei, HE Chang-rong SEISMOLOGY AND GEOLOGY    2024, 46 (2): 235-250.   DOI: 10.3969/j.issn.0253-4967.2024.02.001 Abstract （447）   HTML （28）    PDF（pc） （2735KB）（301）       Knowledge map    Save Serpentine minerals are among the minerals commonly found in the Earth’s subduction zones, and their unique physicochemical properties have a significant impact on subducting geodynamics. Friction experimental studies of serpentine minerals are essential to gain a deep understanding of the frictional sliding stability of serpentine-containing faults in subduction zones as well as explaining the complicated misalignment behavior of faults in subduction zone. Previous laboratory research has produced an abundance of results, and this work addresses two main aspects: the stable states of occurrence and interconversion relationships of serpentine minerals, and the parameters affecting the frictional strength and sliding stability of serpentine minerals. First of all, studies on the stable endowment state of serpentine minerals and the interconversion relationship show that different types of serpentines diaplay different stable phases under different conditions. Chrysotile and lizardite are stable at low temperatures, and the stability fields of both chrysotile and lizardite roughly overlap, but chrysotile is in a substable state. Antigorite is stable at high temperature conditions, such as subduction zone mantle wedges containing high pore fluid pressure conditions, and undergoes a transition from lizardite to antigorite with increasing temperature. Secondly, studies on the factors controlling the frictional strength and sliding stability of serpentine minerals have shown that temperature, pore fluid, and the effective normal stress are all critical factors, for example, an increase in temperature can significantly increase the frictional strength of lizardite and chrysotile. In addition, the friction strength of serpentine minerals shows an obvious pressure dependence, and it was found through previous experimental studies that the friction strength of chrysotile exhibits a high-pressure sensitivity, and that the friction strength of antigorite gradually increases with increasing temperature under low fluid pressure conditions, showing an obvious temperature strengthening phenomenon. In contrast, the change in frictional strength of antigorite with temperature under high-pressure fluid pressure conditions is diametrically opposed to the results of low-pore fluid pressure conditions, which shows a clear temperature weakening phenomenon. Previous studies have also found that antigorite-undergoes a dehydration reaction with increasing temperature under lower fluid pressure conditions, and then exhibits unstable velocity weakening phenomenon, while antigorite exhibits velocity weakening phenomenon under low shear deformation rate under high-pressure fluid conditions. By analyzing the variation of friction-slip stability of antigorite with the shear slip rate can help us to better explain the phenomenon of subduction-zone slow-slip. Overall, experimental studies of the friction of serpentine minerals provide a key experimental basis for a deep understanding of subduction zone geologic processes. The results of these studies are scientifically important for predicting earthquakes and explaining the evolution of the Earth’s internal tectonics and subduction zones, providing strong support for research and practice in the field of geosciences. Table and Figures | Reference | Related Articles | Metrics

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SURFACE DEFORMATION CHARACTERISTICS AND CAUSES OF THE DENGMECUO SEGMENT IN THE XIZANG DINGRI MS6.8 EARTHQUAKE LIANG Ming-jian, DONG Yun-xi, ZUO Hong, DAI You-lin, XIAO Ben-fu, LIAO Cheng, TAN Ling, WANG Yu-wei, LI Xiang, TANG Cai-cheng, ZHANG Wei, ZHANG Hui-ping, MENG Ling-yuan, SU Jin-rong, WU Wei-wei, LI Chuan-you, YAN Mei SEISMOLOGY AND GEOLOGY    2025, 47 (1): 80-89.   DOI: 10.3969/j.issn.0253-4967.2025.01.006 Abstract （1203）   HTML （26）    PDF（pc） （5804KB）（299）       Knowledge map    Save On January 7, 2025, an MS6.8 earthquake struck Dingri, Xizang, China. According to the focal mechanism solution provided by the USGS, this event was characterized as a normal faulting earthquake. The earthquake occurred in the southern segment of the Shenzha-Dingjie Rift system, which is located on the Qinghai-Tibet Plateau. This rift system is one of the seven major rift systems in the southern part of the Tibetan plateau and is a significant controlling structure for shallow-source seismic activity within the region. Moderate to major earthquakes in the study area are primarily distributed along these rift systems. Notably, the Yadong-Gulu Rift system experienced an M8.0 earthquake in 1411 near the southern part of Dangxiong. The seismogenic fault of the earthquake is the Dengmecuo fault, which produced a 26-km-long surface rupture and deformation zone. The Dengmecuo fault is a branch of the southern segment of the Shenzha-Dingjie fault zone and is a Holocene active fault that controls the eastern boundary of the Dengmecuo Basin. The characteristics of the surface deformation zone in this earthquake differ between its northern and southern segments. The northern segment's surface rupture is primarily characterized by normal faulting, with a vertical co-seismic displacement of 2-3 meters. In contrast, the southern segment(the Dengmecuo segment)is mainly distributed on the eastern side of Dengmecuo Lake, with a width exceeding a hundred meters. The deformation characteristics of this segment are complex, exhibiting both extensional and compressional deformations. The extensional deformation zones in the southern segment, which align with the NNE-trending fault scarp, likely represent the tectonically seismogenic surface rupture zone of this earthquake. The compressive deformation zones, however, are believed to have formed as a result of the extensional deformation during the earthquake. These zones are influenced by seismic motion, local terrain, sedimentary characteristics, and climatic conditions and are not directly related to the fault's activity during the earthquake. The differences in the characteristics of the northern and southern segments of the surface deformation zone highlight the complexity of the geometric structure and motion properties of the Dengmecuo fault. Moreover, the main surface deformation zone in the southern section does not align with the surface traces of the Dengmecuo fault, suggesting that the fault may be gradually developing inward into the basin. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON SEISMOGENIC TECTONICS OF THE 2025 MYANMAR MS7.9 EARTHQUAKE XU Bin-bin, ZHANG Yi-peng, LU Le-jun, TIAN Qing-ying, YANG Xue, WANG Yang, ZHANG Pei-zhen SEISMOLOGY AND GEOLOGY    2025, 47 (2): 649-670.   DOI: 10.3969/j.issn.0253-4967.2025.02.20250089 Abstract （560）   HTML （40）    PDF（pc） （13633KB）（292）       Knowledge map    Save According to the China Earthquake Networks Center, an MS7.9 earthquake(hereafter referred to as the Myanmar earthquake)struck the Mandalay region of Myanmar(21.85°N, 95.95°E)on March 28, 2025, at a focal depth of 30km. The earthquake occurred along the central segment of the Sagaing Fault and was characterized by a right-lateral strike-slip rupture, generating a ~350km-long surface rupture zone with a maximum coseismic horizontal displacement of 6 meters. The event caused extensive damage to buildings and varying degrees of destruction to infrastructure, including roads and bridges. Situated in a critical tectonic region where the Indian Plate obliquely converges with the Eurasian Plate, the Myanmar earthquake offers valuable insights into plate boundary deformation processes. Detailed analysis of this event enhances our understanding of the deformation mechanisms along the Myanmar plate boundary and provides essential constraints for seismic hazard assessment along the southeastern margin of the Eurasian Plate. This research holds scientific significance for elucidating continental lithospheric deformation in response to oblique plate convergence. The findings contribute to regional early warning strategies and disaster mitigation efforts and offer a valuable reference for seismic risk studies in comparable tectonic settings worldwide. This study integrates Global Navigation Satellite System(GNSS)data from across the Sagaing Fault region, establishing a comprehensive GNSS velocity field for Myanmar and addressing previous gaps in coverage along the fault’s southern segment. Using multiscale spherical wavelet analysis and GNSS velocity profiles, we examine the deformation characteristics of the region. We calculate the slip rate deficit distribution along the Sagaing Fault and assess postseismic Coulomb stress changes. Combined with historical seismicity data, we investigate the seismogenic structure and stress perturbations in surrounding areas. The key findings are as follows: (1)The Myanmar MS7.9 earthquake was a right-lateral strike-slip event along the central Sagaing fault. The region is affected by the northeastward oblique convergence of the Indian Plate and southeastward extrusion of crustal material from the Tibetan plateau, resulting in strong north-south shear and east-west shortening. The Sagaing fault accommodates most of this deformation, with a rapid right-lateral slip rate of approximately 21~22mm/a. (2)High-resolution GNSS velocity profiles indicate significant fault locking at depths of 15~25km along the Sagaing Fault. The slip rate deficit analysis reveals a high locking ratio across the fault, indicating elevated seismic potential. Notably, the central segment shows lower seismic moment accumulation compared to the northern and southern segments, forming a ~300km-long seismic gap since 1900, capable of generating earthquakes exceeding magnitude 7.5. (3)Coulomb stress modeling suggests that the earthquake significantly altered the regional stress field. Stress accumulation zones were identified at both ends of the Sagaing fault and in the central Shan Plateau to the east. These regions of increased stress transfer and loading exhibit heightened potential for future large earthquakes, underscoring the need for enhanced seismic monitoring. Table and Figures | Reference | Related Articles | Metrics

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RECONSTRUCTION OF THE PALEOCONE MORPHOLOGY OF CHANGBAISHAN TIANCHI VOLCANO MA Chen-yu, CHENG Tao, WAN Yuan, PAN Bo, ZHOU Bing-rui, YAN Li-li SEISMOLOGY AND GEOLOGY    2024, 46 (6): 1248-1262.   DOI: 10.3969/j.issn.0253-4967.2024.06.002 Abstract （810）   HTML （25）    PDF（pc） （5289KB）（278）       Knowledge map    Save Calderas, large basin-shaped landforms created by massive explosive eruptions, leave behind “pot-like” structures that can provide essential insights into the history and processes of volcanic development and associated hazards. The Changbaishan Tianchi caldera, located on the Sino-North Korean border in eastern Jilin Province, China, is one of the best-preserved large Cenozoic composite active volcanoes in China. This caldera, close to the Wangtiane and Baotaishan volcanoes to the south and southeast, sits atop a basalt plateau, reaching a peak elevation of 2 749m. Its formation involved multiple phases of overflow eruption activities, followed by caldera collapse due to explosive eruptions and pressure loss within the crustal magma chamber during the late Pleistocene. Over time, glaciers and flowing water have sculpted its surroundings, creating U-shaped valleys along the caldera rim. The structure and formation processes of its paleocone have thus attracted significant attention. In this study, we drew from reconstruction techniques applied to similar calderas globally. Starting with a focus on the volcanic cone profile, we identified large-scale stratovolcanoes with symmetrical cone shapes akin to Changbaishan Tianchi for comparison. Using high-resolution stereo imagery, we extracted a Digital Elevation Model(DEM)with remote sensing software. From these DEMs, we performed detailed topographic analysis, calculating and statistically modeling geomorphological parameters, which allowed us to develop a three-phase empirical model of cone topography. Applying a moving surface algorithm in MATLAB, we generated surface equations for each volcano profile, revealing quantitative relationships between pixel position, coordinates, and elevation in 3D geographic space. We then used ArcGIS's Kriging interpolation method to create a DEM of the reconstructed cone of Changbaishan Tianchi volcano, allowing us to approximate the original cone structure. The results estimate the original Changbaishan Tianchi cone reached a height of 4, 100m, with a crater diameter of about 390m and a depth of 170m. The cone displayed a funnel-like structure at the summit, with slopes characteristic of stratovolcanoes. The inner edge of the cone had a relatively uniform slope, while the upper outer edge was steep, averaging 27°, and the lower outer slope angle decreased to an average of 18.5°. These parameters align with typical stratovolcano profiles. The explosive eruptions and subsequent cone collapse are estimated to have led to a volume loss of approximately 28.92km3. This paleocone reconstruction of Tianchi volcano enhances our understanding of the history of the development and evolution of Tianchi volcano, contributing valuable data for reconstructing similar caldera cones and examining eruption mechanisms within the Changbaishan volcanic field. Moreover, this study provides critical information for analyzing the geological history of Tianchi volcano, including the formation of glacial landforms and processes related to eruptions and natural disasters. Table and Figures | Reference | Related Articles | Metrics

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3D STRUCTURAL MODELLING OF THE ANNINGHE-ZEMUHE-XIAOJIANG FAULT ZONE IN THE EASTERN BOUNDARY OF SICHUAN-YUNNAN BLOCK USING MULTI-DATA AND IMPLICIT MODELING METHODS WANG Mao-mao, HU Shun-yang, MA Hao-ran, LIANG Bo-yu, ZHANG Jin-yu, LU Ren-qi SEISMOLOGY AND GEOLOGY    2024, 46 (1): 19-34.   DOI: 10.3969/j.issn.0253-4967.2024.01.002 Abstract （517）   HTML （31）    PDF（pc） （8144KB）（273）       Knowledge map    Save The Anninghe-Zemuhe-Xiaojiang fault zone is located at the intersection between the Qinghai-Xizang Plateau and the Yangtze block, representing the eastern boundary of the Sichuan-Yunnan block with frequent seismic activities. Its overall kinematic characteristics involve left-lateral strike-slip motion, and the fault structures along its strike are complex, posing significant challenges in accurately characterizing the 3D structural features of deep faults. The main issues include the structural complexity of the fault surfaces, uncertainties in the intersection relationships of fault systems, spatial constraints of blind faults, and the definition of fault surfaces in regions with weak seismic activity. Traditionally, 3D structural modeling for fault geometry heavily relies on high-resolution seismic reflection profiles, 3D seismic data volumes, and borehole data. It defines the geometric shapes of objects with limited nodes in a triangular mesh, and then simulates the topological structure of objects by connecting these nodes. However, obtaining high-resolution seismic reflection data in active tectonic areas like the eastern boundary of the Sichuan-Yunnan block is challenging, and even when available, it is often sparse in space. Alternatively, a large amount of relocated earthquakes and surface fault traces are generally used to create initial three-dimensional models of active faults. However, this approach overlooks the contributions of focal mechanism solutions in constraining the modeling, with more subjectivity in the selection of relocated seismicity, and does not adopt a differentiated weight strategy for various data sources. In this study, a 3D implicit modeling approach, combining deep and shallow geological and geophysical data that are generally available in active tectonic environments, was used to construct a detailed 3D structural model of the Anninghe-Zemuhe-Xiaojiang fault zone at the eastern boundary of the Sichuan-Yunnan block. The modeling process effectively integrated the fault plane constraints provided by focal mechanism solutions with surface fault traces and relocated seismic data, using a multi-iteration process with differentiated weight to increase the accuracy of the fault models. This approach ultimately represented the 3D complex structural features of the eastern boundary of the Sichuan-Yunnan block using multiple data sources. The modeling results show that the Anninghe-Zemuhe fault zone is characterized by a steep strike-slip fault structure with along-strike geometry variations. The Anninghe Fault shows its steepest dip angle in the central segment and gradually becomes gentler to both ends. Meanwhile, the Zemuhe Fault exhibits several asperities that are perpendicular to the direction of fault slip at a depth of 5~15km. By contrast, the north-to-central segment of the Xiaojiang fault zone is more complex. The western branch of the Xiaojiang Fault, which is an east-dipping, left-lateral strike-slip fault, is characterized by a relatively gentle fault plane with an average dip angle of 76° to 78°. The west-dipping segment of the eastern Xiaojiang Fault has a steeper dip with an average angle of 85°. The detailed 3D structural model of active faults constructed through implicit modeling can be used for analyzing fault roughness and fault system studies, which are crucial for understanding the distribution of asperities on fault planes and conducting seismic rupture simulations. Implementing the implicit modeling approach allows for the development of improved fault surface representations that can contribute to Community Fault Models in active tectonic environments, and support fault system modeling, rupture simulations, and regional hazard assessments. Table and Figures | Reference | Related Articles | Metrics

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RELOCATION OF THE 2022 MS6.0 MAERKANG EARTHQUAKE SWARM IN SICHUAN PROVINCE AND ITS SEISMIC FAULT ANALYSIS XU Ying-cai, GUO Xiang-yun SEISMOLOGY AND GEOLOGY    2023, 45 (4): 1006-1024.   DOI: 10.3969/j.issn.0253-4967.2023.04.012 Abstract （471）   HTML （35）    PDF（pc） （13832KB）（273）       Knowledge map    Save The 2022 MS6.0 Maerkang earthquake swarm in Sichuan Province is the first rare strong swarm activity with high frequency, concentrated spatial and temporal distribution, strong explosive and strong magnitude in Maerkang area in the eastern segment of Bayan Har block in China seismic network records. It is also another significantly strong earthquake event in Bayan Har block after the MS7.4 Maduo earthquake on May 22, 2021. The MS6.0 Maerkang earthquake on June 10, 2022 not only broke the 33-year record without MS≥6.0 earthquakes within 100km of the epicenter, but also broke the historical record without MS≥6.0 earthquakes within 50km of the epicenter. The earthquake swarm is mainly located in the nearly “T” shaped conjugate fault structure area composed of the NW strike Maerkang fault and NE strike Longriba fault in the Bayan Har block. This area is a relatively rare region for moderate and strong earthquakes in the history. Therefore, it is of great significance to analyze and discuss the possible seismogenic faults of the Maerkang strong earthquake sequence for the study of seismogenic structures and the risk of strong earthquakes in the weak seismic region of Bayan Har block. The earthquake swarm was relocated by double-difference method, and focal mechanisms and centriod depths of MS≥3.6 earthquakes were calculated by using gCAP inversion method. Then the relationship between the stress system in the Malkang area and these earthquake focal mechanisms was analyzed, and fault plane was fitted by using relocation results. Maerkang earthquake swarm is mainly distributed along NW direction, and the initial rupture depth is 9.8km on average. Depth profiles show that earthquakes are mainly concentrated at depth between 0km to 15km. The most earthquakes of early-stage occurred in 48 hours. The mid-stage and late-stage earthquakes are located less than 15km in depth and move to the northwest of the epicenters. Initial rupture depth of the largest MS6.0 earthquake is 12.5km, which is almost at the bottom of the dense area. The focal mechanism of MS6.0 earthquake is 150° in strike, 79° in dip, and 7° in rake on nodal plane Ⅰ, and 59° in strike, 83° in dip, and 169° in rake on nodal plane Ⅱ, with the centroid depth of 9km. Other focal mechanisms of MS≥3.6 earthquake are strike-slip types. Dips of nodal plane of focal mechanism range from 71° to 86°, and there exist different dip directions for one strike of every nodal plane. All azimuths of P axis are in NWW direction, and the plunges are nearly horizontal. The focal mechanisms of MS≥3.6 earthquakes show that the tectonic environment is very favorable for NE or NW strike faults to generate the strike-slip movement. Centriod depths range from 5 to 9km, which are lower than the average depth of 9.8km of relocation, indicating that these earthquakes mainly ruptured from deep to shallow. The relative shear stress of the NW nodal plane are significantly greater than that of the NE nodal plane, and the normal stress of the NW nodal plane was smaller than that of the NE nodal plane, indicating more possibility of strike-slip dislocation on the NW nodal plane. The fault plane fitting results reveal that there are obviously two nearly parallel and nearly NW strike earthquake belts in the epicenter area. Fitted fault plane parameters of the belt in the north branch show the strike 333°, the dip 88°, the slide -22°, and the belt in the south branch show the strike 331°, dip 88°, and slide -23°. It is indicated that the fault properties of these two earthquake belts are basically the same, revealing that most of earthquake activities of the swarm may be controlled by at least two parallel structures near the Maerkang fault with the NW strike, dip 88° and left-lateral strike-slip. Combined with the existing regional geological structure, it is inferred that the Maerkang earthquake swarm may be induced by the NW and NE strike conjugate faults, and the NW strike faults control most of the earthquake activities. Table and Figures | Reference | Related Articles | Metrics

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PRECISE LOCATION AND SEISMOGENIC STRUCTURE OF THE 2022 LUSHAN MS6.1 EARTHQUAKE FU Ying, HU Bin, ZHAO Min, LONG Feng SEISMOLOGY AND GEOLOGY    2023, 45 (4): 987-1005.   DOI: 10.3969/j.issn.0253-4967.2023.04.011 Abstract （625）   HTML （28）    PDF（pc） （7950KB）（272）       Knowledge map    Save On June 1, 2022, a MS6.1 earthquake occurred in Lushan, Sichuan Province, western China, which is approximately 10km from the Lushan MS7.0 event on April 20, 2013. To understand if the earthquake has the same seismogenic structure as the Lushan MS7.0, we relocated the event in the Lushan area using the multi-stage locating method based on the seismic phase arrival data of the Sichuan Seismic Network from April 20, 2013, to July 1, 2022. A total of 6992 ML≥1.0 earthquakes were acquired, with a relative locating error of 0.5km and 0.7km in the horizontal and vertical directions, respectively, with a travel time residual(RMS)of 0.18s. The results show that the MS6.1 event is located at 102.943°E, 30.382°N with an initial-rupture focal depth of 15.6km, lying on the NW side of the 2013 Lushan MS7.0 event. The sub-surface rupture length of the long and short axis is 10 and 8km, measured from the dense aftershock area in NE-SW and NW-SE directions, respectively. The NE-SW profile in the Lushan area shows that the depth of Lushan MS7.0 earthquake in 2013 was about 15km, similar to that of Lushan MS6.1 and MS4.5 on June 1, 2022. The MS6.1 earthquake sequence, located at the NE end of the long axis, shows no evidence to break through the rupture termination point of the Lushan MS7.0 earthquake and enters the Dayi seismic gap, which is bounded by the 2008 Wenchuan MS8.0 and 2013 Lushan MS7.0 aftershock regions. The short-axis profile shows that the MS6.1 earthquake sequence occurred on a new back-thrust fault in the pre-existing seismogenic structure of the 2013 Lushan MS7.0. The new structure dips SE and ruptures in a slight arc protruding into the NW, parallel to the northern segment of the seismogenic structure of the 2013 Lushan MS7.0 earthquake with a horizontal distance of about 5km. The new and old structures connect at the detachment base to the main segment of the 2013 Lushan MS7.0 earthquake. We also inverted the focal mechanism of the Lushan MS6.1 earthquake using the CAP(Cut and Paste)method. The result indicates that the centroid depth of the MW5.7 main event is 14km which is very close to the initial-ruptured depth of 15km calculated by the phase arrival times. The best double couple parameters are 221°/40°/105° for nodal plane Ⅰ and 22°/52°/78° for nodal plane Ⅱ. The parameters are in order of the strike, dip, and rake angles. Combined with the realization of the NE-striking, SE-dipping seismogenic structure characteristics determined by the accurate locating of the earthquake sequence, it can be quickly confirmed that the nodal plane Ⅱ is the fault plane. Based on the accurate locating results, focal mechanism solutions, and geodynamic background of the focal area, it is inferred that the seismogenic structure of the Lushan MS6.1 earthquake is induced by the thrust dislocation of a NE-SW trending and SE inclining thrust fault in the southern section of Longmenshan fault zone. Finally, we discussed the relationship between MS7.0 and MS6.1 in the Lushan area. The two could be considered a unique sequence: the mainshock and the maximum aftershock, respectively, regarding spatial relationship and tectonic correlation. However, the time interval of these two earthquakes significantly overextends the statistical relationship between the principal earthquake and the maximum aftershock. Furthermore, considering the effects of the Coulomb stress change produced by the earthquakes repeated at the end of the Dayi gap, Lushan earthquake further enhanced the stress level in the Dayi seismic gap located in its northern segment. Table and Figures | Reference | Related Articles | Metrics

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GRAIN SIZE AND MICROSTRUCTURE CHARACTERISTICS OF HOLOCENE MEGAFLOOD SLACK WATER DEPOSITS IN THE MIDDLE REACHES OF THE YARLUNG TSANGPO RIVER XU Bo, WANG Ping, WANG Hui-ying, GUO Qiao-qiao, SHI Ling-fan, SHI Yu-xiang SEISMOLOGY AND GEOLOGY    2023, 45 (2): 305-320.   DOI: 10.3969/j.issn.0253-4967.2023.02.001 Abstract （496）   HTML （27）    PDF（pc） （6489KB）（270）       Knowledge map    Save The terrain in southeastern Tibet is steep and the valleys are crisscrossed. Since the Quaternary, glacial ice and debris have blocked the course of the Yarlung Tsangpo River and its tributary river valleys to form giant dammed lakes, and the huge flood deposits formed by the dammed lake outburst floods are often associated with moraines, ice water deposits, lacustrine deposits, aeolian sand or other running water sediments to form complex river valley accumulation landforms. Different types of sediments in alpine and canyon areas are similar in morphology, structure and fabric, and are difficult to distinguish. Grain size and morphological characteristics are the most important structural characteristics of sediment, and the distribution rules are controlled by many factors such as sedimentary environment, physical properties of detrital material, transporting medium and transporting mode, etc., which is an important proxy index for restoring paleoclimate and inverting paleoenvironment. However, the relevant research on identifying sediment types in alpine valley area of southeast Tibet by grain size and morphology index is still in the exploratory stage. In order to understand the particle size characteristics and spatial differentiation laws of outburst flood sediments and the micromorphological characteristics of particle surfaces, we collected 33 samples of Holocene flood retention sediments preserved along the river within about 350km from the outlet of the Jiacha Gorge in the middle reaches of the Yarlung Tsangpo River to Pai Town, and measured them with Malvern 3000 laser diffraction particle size meter and Zeiss Signma scanning electron microscope, combined with digital geomorphology(DEM)data extracted river channel width and steepness coefficient. The features of spatial distribution law of particle size are analyzed, and the following understanding is obtained. The particle size of outburst flood retention deposits is characterized on the whole by fine-silty sand(2.57~5.18Φ)with poor sorting, positive skew and narrow peak state. Two end element models are obtained: The main peak of EM1 terminal element is 3.16Φ, with an average percentage content of 42.7%, which may represent the alluvial characteristics of higher energy of outburst floods in alpine valley areas, and the main peak of EM2 terminal elements is 2.06Φ with an average percentage content of 55.6%, which can be used to indicate the accumulation process of the outburst flood lag deposits. Affected by the width of the river, the EM1 content has a tendency to increase downstream, while EM2 has the opposite trend. The surface microstructure of quartz particles in the outburst flood lag deposits is mainly characterized by mechanical scratches, shell-like fractures, upturn cleavage and cleavage steps, with low structural maturity, mostly angular shape, and rare denudation pores of chemical origin. As a typical representative of climbing sand dunes in the valley area of the semi-humid monsoon area, the genesis of the dunes is of great guiding significance for revealing the source of sand dunes in the valley area of the alpine valley area, identifying paleoflood deposit and aeolian deposit, distinguishing aeolian deposit and paleoflood slackwater deposits on both sides of the riverbank, and windbreak and sand fixation engineering in the Yarlung Tsangpo River. By comparing the particle size and surface micromorphology characteristics of the known outburst flood deposits of the Yarlung Tsangpo River, we believe that the sand source of the Fozhang dunes is mainly from the outburst flood deposits and was transformed later by wind forces. Table and Figures | Reference | Related Articles | Metrics